CHEMICALS OF THE NATURAL ENVIRONMENT C5 21 ST CENTURY SCIENCE

Definitions The atmosphere The lithosphere The hydrosphere The biosphere Mixture of gases that surround the Earth. It includes oxygen we need to survive and water vapour. 78% N 2 , 20% O 2 , 1% Ar. Solid crust and top part of mantle, contains rocks and mantle we use for raw materials. All the water on the surface of the Earth (oceans, seas, rivers and lakes) and the chemicals dissolved in them. Includes all living things including plants and animals

The atmosphere

The lithosphere

The hydrosphere

The biosphere

Mixture of gases that surround the Earth. It includes oxygen we need to survive and water vapour. 78% N 2 , 20% O 2 , 1% Ar.

Solid crust and top part of mantle, contains rocks and mantle we use for raw materials.

All the water on the surface of the Earth (oceans, seas, rivers and lakes) and the chemicals dissolved in them.

Includes all living things including plants and animals

LEARNING OBJECTIVES L1 be able to describe the basic structures of the Earth. know the meaning of the terms atmosphere, hydrosphere, lithosphere and biosphere. understand what types of chemicals make up the Earth’s lithosphere. understand that a chemical’s properties, bonding and structure will affect where it is found. By the end of the lesson you should:

be able to describe the basic structures of the Earth.

know the meaning of the terms atmosphere, hydrosphere, lithosphere and biosphere.

understand what types of chemicals make up the Earth’s lithosphere.

understand that a chemical’s properties, bonding and structure will affect where it is found.

The Structure of the Earth The average density of the Earth is much higher than the crust, so the inner core must be very dense A thin crust - 10-100km thick A mantle – has the properties of a solid but it can also flow A core – made of molten nickel and iron. Outer part is liquid and inner part is solid

What do you know about the Earth? Put the following list of Earth facts in order of size, starting with the largest thing first! Don’t panic: you only need to guess.

Put the following list of Earth facts in order of size, starting with the largest thing first!

Don’t panic: you only need to guess.

Put these Earth facts in order of size A The height of the tallest MOUNTAIN B The depth of the Earth’s ATMOSPHERE C The depth of the deepest OCEAN D The depth of the Earth’s CRUST E The depth of the deepest LAKE

Were you right? B The depth of the Earth’s ATMOSPHERE D The depth of the Earth’s CRUST C The depth of the deepest OCEAN A The height of the tallest MOUNTAIN E The depth of the deepest LAKE

The Earth is the source of all our materials. We can get things from: the atmosphere the lithosphere the biosphere the hydrosphere Chemicals from the Earth’s spheres

The Earth is the source of all our materials.

We can get things from:

the atmosphere

the lithosphere

the biosphere

the hydrosphere

Elements and compounds are constantly moving between the spheres in which they are found. Water and carbon dioxide are absorbed by plants for photosynthesis from the atmosphere to be part of the biosphere. Minerals and salts in the soil dissolve in rainwater and are washed into the hydrosphere. Fuels found in the lithosphere are burned and the gases released are released into the atmosphere.

Elements and compounds are constantly moving between the spheres in which they are found. Water and carbon dioxide are absorbed by plants for photosynthesis from the atmosphere to be part of the biosphere. Minerals and salts in the soil dissolve in rainwater and are washed into the hydrosphere. Fuels found in the lithosphere are burned and the gases released are released into the atmosphere.

Chemical bonding Where chemical are found depends on their properties and their properties depend on how their atoms are joined together. Chemical bonds are forces that join atoms together

Where chemical are found depends on their properties and their properties depend on how their atoms are joined together. Chemical bonds are forces that join atoms together

Use the data table to fill in the table

Where on Earth For each character use the speech bubble to describe some physical properties of materials which are found there. Think about the physical state of the materials, their melting points (high or low) and their solubility.

For each character use the speech bubble to describe some physical properties of materials which are found there. Think about the physical state of the materials, their melting points (high or low) and their solubility.

Movement of the Lithosphere The Earth’s LITHOSPHERE (i.e. the _______) is split up into different sections called ________ plates: Words – radioactive, crust, convection, tectonic, year These plates are moving apart from each other a few centimetres every _______ due to the ________ currents in the mantle caused by the ________ decay of rocks inside the core.

LEARNING OBJECTIVES L2 be aware that dry air consists of gases, some of which are elements (oxygen, nitrogen and argon) and some of which are compounds (carbon dioxide). understand that most non-metal elements are molecular. understand that most compounds formed between non-metal elements are molecular. be able to use data to show that molecular elements and compounds generally have low melting and boiling points. know that the elements and compounds in the air are gases because they consist of small molecules with weak forces of attraction between the molecules. By the end of the lesson you should:

be aware that dry air consists of gases, some of which are elements (oxygen, nitrogen and argon) and some of which are compounds (carbon dioxide).

understand that most non-metal elements are molecular.

understand that most compounds formed between non-metal elements are molecular.

be able to use data to show that molecular elements and compounds generally have low melting and boiling points.

know that the elements and compounds in the air are gases because they consist of small molecules with weak forces of attraction between the molecules.

N 2 is a very unreactive gas. It makes up 78% of the air. O 2 makes up 21% of the air. Ar is one of the noble gases. It is very unreactive. It makes up 1% of the air. CO 2 makes up only 0.03% of the air. H 2 O is present in moist air. Water cycles between the four spheres. All living things remove O 2 from the air by respiration. O 2 is given out by green plants in sunlight. It is a product of photosynthesis. CO 2 is given out by all living things during respiration. CO 2 is taken in by plants during photosynthesis. Nitrogen is not completely inert. During thunderstorms some N 2 reacts with O 2 . The products are washed out of the air by rain. This can add nitrates to soil. Volcanoes are a natural source of gases which cause pollution.

What happens to air pollutants? CO 2 is absorbed by plants. Particulate carbon is deposited on surfaces, making them dirty. Ozone, O 3 , is a secondary pollutant produced in the lower atmosphere. SO 2 and NO 2 react with water vapour in the atmosphere to make ‘acid rain’. CO is very poisonous and remains unchanged for some time. NO turns rapidly to the secondary pollutant NO 2 . CO 2 dissolves in the oceans.

Attractive forces between molecules are weak. Small molecules are gases or liquids at room temperature.

Attractive forces between molecules are weak.

Small molecules are gases or liquids at room temperature.

The bonds inside molecules are strong. Water molecules do not fall apart when the liquid boils and turns to steam. water molecule water molecule

The bonds inside molecules are strong.

Water molecules do not fall apart when the liquid boils and turns to steam.

Electron Configurations What is the electron configuration of the following (atomic number in brackets): Hydrogen (1) Lithium (3) Carbon (6) Nitrogen (7) Aluminium Atomic number = number of protons = number of electrons

What is the electron configuration of the following (atomic number in brackets):

Hydrogen (1)

Lithium (3)

Carbon (6)

Nitrogen (7)

Aluminium

LEARNING OBJECTIVES L3 be able to describe a covalent bond as a pair of electrons shared between two atoms. be aware that the covalent bonding within molecules is strong and it arises from the electrostatic attraction between the nuclei of the atoms and their shared electrons. understand that pure molecular compounds do not conduct electricity because molecules are not charged. be aware that the molecules water and carbon dioxide have a definite shape which chemists represent with molecular models. be able to use representations of molecules including: molecular formulae 2-D diagrams in which covalent bonds are represented by lines 3-D diagrams for elements that are gases at 20 °C and simple molecular compounds. By the end of the lesson you should:

be able to describe a covalent bond as a pair of electrons shared between two atoms.

be aware that the covalent bonding within molecules is strong and it arises from the electrostatic attraction between the nuclei of the atoms and their shared electrons.

understand that pure molecular compounds do not conduct electricity because molecules are not charged.

be aware that the molecules water and carbon dioxide have a definite shape which chemists represent with molecular models.

be able to use representations of molecules including:

molecular formulae

2-D diagrams in which covalent bonds are represented by lines

3-D diagrams

for elements that are gases at 20 °C and simple molecular compounds.

Attractive forces between molecules are weak. Small molecules are gases or liquids at room temperature.

Attractive forces between molecules are weak.

Small molecules are gases or liquids at room temperature.

The bonds inside molecules are strong. Water molecules do not fall apart when the liquid boils and turns to steam. water molecule water molecule

The bonds inside molecules are strong.

Water molecules do not fall apart when the liquid boils and turns to steam.

How are the atoms in an H 2 molecule held together? To picture this you need to look at the structure of a hydrogen atom. The positively charged nucleus and the negatively charged electron attract each other.

How are the atoms in an H 2 molecule held together?

To picture this you need to look at the structure of a hydrogen atom.

The positively charged nucleus and the negatively charged electron attract each other.

When two hydrogen atoms approach each other . . . . . . the electron of one atom and the nucleus of the other atom start to attract each other.

When two hydrogen atoms approach each other . . .

. . . the electron of one atom and the nucleus of the other atom start to attract each other.

When the atoms are close, the attractions are so strong that a molecule of hydrogen (H 2 ) is formed. The atoms are held together by the attractions between the two nuclei and the shared pair of electrons. This is a single covalent bond.

When the atoms are close, the attractions are so strong that a molecule of hydrogen (H 2 ) is formed.

The atoms are held together by the attractions between the two nuclei and the shared pair of electrons. This is a single covalent bond.

Chemists draw a line between element symbols to show a covalent bond. H—H hydrogen, H 2 O O oxygen, O 2 N N nitrogen, N 2 O C O carbon dioxide, CO 2 H H—C—H H methane, CH 4 H H H—C—C—O—H H H ethanol, C 2 H 5 OH O H H water, H 2 O

Covalent bonding in chlorine Chlorine (2.8.7) needs 1 more electron to have a completely full outer shell. To achieve this, it can share an electron with another chlorine atom. This creates a single bond. Cl Cl Cl 2 or Cl–Cl Cl

Covalent bonding in oxygen Oxygen (2.8.6) needs 2 more electrons to have a completely full outer shell. To achieve this, it can share two electrons with another oxygen atom. This creates a double bond . O O 2 or O=O O O O

Covalent bonding in nitrogen Nitrogen (2.8.5) needs 3 more electrons to have a completely full outer shell. It can share three electrons with another nitrogen atom to do this. This creates a triple bond . N 2 or N ≡N N N N N

Covalent bonding in methane How are carbon and hydrogen bonded in methane? 2.4 1 4 1 1 4 Ratio of atoms Electrons needed Electron configuration H C CH 4 or H C H H H C H H H H

Chemists have different ways of describing molecules. molecular formula displayed formula with lines for covalent bonds ball-and-stick model space-filling model

What are the electron configurations of Sodium (Gp 1) and Chlorine (Gp 7)? What is the charge of a chloride ion? What is the charge of a sodium ion?

LEARNING OBJECTIVES L4 be aware that the Earth’s hydrosphere consists mainly of water with some dissolved compounds. know that the weathering of rocks in the lithosphere produces a range of chemicals some of which are soluble salts. be aware that seawater is ‘salty’ because it contains dissolved ionic compounds called salts. By the end of the lesson you should:

be aware that the Earth’s hydrosphere consists mainly of water with some dissolved compounds.

know that the weathering of rocks in the lithosphere produces a range of chemicals some of which are soluble salts.

be aware that seawater is ‘salty’ because it contains dissolved ionic compounds called salts.

Sun evaporation condensation rain rivers weathering of rocks followed by dissolving of soluble salts solutions of soluble salts and sediment end up in the sea

What is so special about water and water molecules? Liquid water consists of H 2 O molecules that are close together but moving randomly. water molecule

What is so special about water and water molecules?

Liquid water consists of H 2 O molecules that are close together but moving randomly.

Ions and electron structures Metals lose electrons to form positive(+) ions called cations. Non-metals gain electrons to form negative (–) ions called anions. We know that the atoms lose or gain electrons to achieve full electron shells. To understand more about how ionic compounds form we must look at what is happening to the outer shell electrons . n + n -

Metals lose electrons to form positive(+) ions called cations.

Formation of sodium chloride 1. Formation of sodium ions Sodium has 1 electron in its outer shell. If it loses this it will have no partially filled shells. Sodium 1+ ion (2.8.0) Sodium atom (2.8.1) This only happens if there is another atom able to accommodate the lost electron. Loses 1 electron Na Na+

Sodium has 1 electron in its outer shell.

Formation of sodium chloride 2.Formation of Chloride ions Chlorine has 7 electrons in its outer shell. If it gains 1 electron it can achieve a full outer electron shell. It is, therefore, going to be able to accept the electron that the sodium wants to lose. Chlorine atom (2.8.7) Chlorine I - ion (2.8.8) Gains 1 electron (from sodium) Cl Cl

Chlorine has 7 electrons in its outer shell.

Bonding in Magnesium Oxide More than one electron may be transferred between atoms in ionic bonding. O Mg 2.8.2. 2.6 Magnesium atom Oxygen atom Mg2+ O2- 2.8 2.8 Magnesium Oxide

More than one electron may be transferred between atoms in ionic bonding.

Draw a simplified bonding diagram (omitting inner shells) for magnesium oxide. Mg O Magnesium atom Oxygen atom Mg2+ O2- Magnesium Oxide

Draw a simplified bonding diagram (omitting inner shells) for magnesium oxide.

Copy the diagram and draw another box showing the electron configuration in sodium fluoride. 2.8 2.8 Sodium Fluoride Sodium atom Fluorineatom Na+ F Na 2.8.1. 2.7 F-

Copy the diagram and draw another box showing the electron configuration in sodium fluoride.

Following the previously shown slides draw bonding diagrams for the compounds formed from the following atoms: Lithium (2.1) and fluorine (2.7) Sodium (2.8.1) and sulphur (2.8.6) Magnesium (2.8.2) and sulphur (2.8.6) Magnesium (2.8.2) and fluorine (2.7) Aluminium (2.8.3) and nitrogen (2.5) Remember that the total number of electrons lost by the metal must equal the total number of electrons gained by the non-metal Activity

Following the previously shown slides draw bonding diagrams for the compounds formed from the following atoms:

Lithium (2.1) and fluorine (2.7)

Sodium (2.8.1) and sulphur (2.8.6)

Magnesium (2.8.2) and sulphur (2.8.6)

Magnesium (2.8.2) and fluorine (2.7)

Aluminium (2.8.3) and nitrogen (2.5)

Water is a liquid at room temperature. Water is a good solvent even for salts.

Water is a liquid at room temperature.

Water is a good solvent even for salts.

+ When NaCl is added to water, the ions are pulled off the structure and they become free to move in the water. The ions can move independently, so a solution of NaCl in water conducts electricity.

When NaCl is added to water, the ions are pulled off the structure and they become free to move in the water.

The ions can move independently, so a solution of NaCl in water conducts electricity.

Salt harvesters in Thailand raking salt into piles

Machinery at work inside a salt mine

A sodium chloride crystal is made up of millions of Na + and Cl – ions arranged in a regular pattern. The regular pattern is responsible for the cubic range of all sodium chloride crystals. Crystals of sodium chloride

A sodium chloride crystal is made up of millions of Na + and Cl – ions arranged in a regular pattern.

The regular pattern is responsible for the cubic range of all sodium chloride crystals.

Oppositely charged ions attract each other. Each ion will attract oppositely charged ions from all directions. Each of these ions will in turn attract more ions. A giant ionic structure made up of millions of ions is built up and forms a sodium chloride crystal.

Oppositely charged ions attract each other.

Each ion will attract oppositely charged ions from all directions.

Each of these ions will in turn attract more ions.

A giant ionic structure made up of millions of ions is built up and forms a sodium chloride crystal.

The Earth’s Structure Beneath the atmosphere the Earth consists of 4 main layers:

LEARNING OBJECTIVES L5 remember that much of the Earth’s silicon and oxygen is present in the Earth’s crust as the compound silicon dioxide. know the properties of silicon dioxide (hardness, melting point, electrical conductivity and solubility in water). be able to explain the properties of silicon dioxide in terms of a giant structure of atoms held together by strong covalent bonding. be aware that silicon dioxide is found as quartz in granite, and is the main constituent of sandstone. be able to predict properties and structures of other giant covalent lattices, like diamond. By the end of the lesson you should:

remember that much of the Earth’s silicon and oxygen is present in the Earth’s crust as the compound silicon dioxide.

know the properties of silicon dioxide (hardness, melting point, electrical conductivity and solubility in water).

be able to explain the properties of silicon dioxide in terms of a giant structure of atoms held together by strong covalent bonding.

be aware that silicon dioxide is found as quartz in granite, and is the main constituent of sandstone.

be able to predict properties and structures of other giant covalent lattices, like diamond.

Just in at number 10 , forming 0.1% is . . . . . . phosphorus . This non-metallic element is found mainly as the mineral phosphate.

Just in at number 10 , forming 0.1% is . . .

. . . phosphorus .

This non-metallic element is found mainly as the mineral phosphate.

At number 9 with 0.5% is . . . . . . titanium . This useful metal is commonly found as the oxides rutile and ilmenite.

At number 9 with 0.5% is . . .

. . . titanium .

This useful metal is commonly found as the oxides rutile and ilmenite.

Almost 1.5% higher, at number 8 with 2.5% is . . . . . . magnesium . Another metallic element, this is found in minerals such as magnesite and dolomite.

Almost 1.5% higher, at number 8 with 2.5% is . . .

. . . magnesium .

Another metallic element, this is found in minerals such as magnesite and dolomite.

Just above magnesium at number 7 is . . . . . . potassium , with 2.6%. This metallic element is found extensively in potash and sylvite.

Just above magnesium at number 7 is . . .

. . . potassium , with 2.6%.

This metallic element is found extensively in potash and sylvite.

Coming in at number 6 with 2.8% is a close relative of potassium – it’s . . . . . . sodium . This is found in a number of minerals but particularly in rock salt or halite.

Coming in at number 6 with 2.8% is a close relative of potassium – it’s . . .

. . . sodium .

This is found in a number of minerals but particularly in rock salt or halite.

Moving up to number 5 with 3.6% is yet another metal . . . . . . calcium . This element is found in limestone and gypsum.

Moving up to number 5 with 3.6% is yet another metal . . .

. . . calcium .

This element is found in limestone and gypsum.

At number 4 with 5% is . . . . . . iron . The most common ore of iron is haematite (iron oxide).

At number 4 with 5% is . . .

. . . iron .

The most common ore of iron is haematite (iron oxide).

Moving in to the top three, at number 3 we have the final metallic element . . . . . . aluminium , with 8.1%. It’s found mainly as the oxide bauxite.

Moving in to the top three, at number 3 we have the final metallic element . . .

. . . aluminium , with 8.1%.

It’s found mainly as the oxide bauxite.

At number 2 is a non-metal . . . . . . silicon , with a mighty 27.7%. Silicon is found as the oxide in quartz, sand, and amethyst, and as silicate minerals such as clay and feldspar.

At number 2 is a non-metal . . .

. . . silicon , with a mighty 27.7%.

Silicon is found as the oxide in quartz, sand, and amethyst, and as silicate minerals such as clay and feldspar.

Finally, in the number 1 spot with an enormous 46.6% is . . . . . . oxygen . Oxygen is a non-metallic gas found in a wide variety of oxide minerals.

Finally, in the number 1 spot with an enormous 46.6% is . . .

. . . oxygen .

Oxygen is a non-metallic gas found in a wide variety of oxide minerals.

The 10 most abundant elements in the continental crust. O Si Al Fe Ca Na K Mg Ti P percentage relative abundance 50 40 30 20 10

Silica shares some properties of both giant ionic and simple covalent structures. metal and non-metal not soluble in water hard crystalline solid low m.p. electrical conductor in solution or molten high m.p. non-metals Silicon Dioxide properties of silicon dioxide properties of substances with giant ionic structures properties of substances with simple covalent molecules

Each silicon atom can make four bonds and each oxygen atom can make two.

An oxygen atom can act as a bridge between two silicon atoms.

This leaves each silicon able to link with three more oxygen atoms.

This in turn allows the oxygen atoms to act as bridges to more silicon atoms and so on. Eventually a giant covalent structure is formed with millions of silicon and oxygen atoms.

This in turn allows the oxygen atoms to act as bridges to more silicon atoms and so on.

Eventually a giant covalent structure is formed with millions of silicon and oxygen atoms.

The many strong covalent bonds in this giant structure make silica a very hard, high melting point solid. This makes it useful for manufacturing materials such as sandpaper and abrasives.

The many strong covalent bonds in this giant structure make silica a very hard, high melting point solid.

This makes it useful for manufacturing materials such as sandpaper and abrasives.

Other giant covalent structures include diamond and graphite.

The properties of diamond All the electrons in the outer shell of the carbon atom (2.4) are used in covalent bonds. This affects diamond’s properties. Diamond is very hard – the hardest natural substance on Earth. Diamond has a very high melting and boiling point – a lot of energy is needed to break the covalent bonds. Diamond cannot conduct electricity – there are no free electrons or ions to carry a charge

Diamond is very hard – the hardest natural substance on Earth.

Diamond has a very high melting and boiling point – a lot of energy is needed to break the covalent bonds.

Diamond cannot conduct electricity – there are no free electrons or ions to carry a charge

The structure of graphite Graphite is a much more common form of carbon. in which each atom is covalently bonded to three others. This forms rings of six atoms, creating a giant structure containing many layers. These layers are held together by weak forces of attraction. weak forces of attraction C C C C

The properties of graphite Only three of the four electrons in the outer shell of the carbon atom (2.4) are used in covalent bonds. This affects graphite’s properties. Graphite is soft and slippery – layers can easily slide over each other because the weak forces of attraction are easily broken. This is why graphite is used as a lubricant. Graphite can conduct electricity – the only non-metal to do. There is a free electron from each atom to carry a charge.

Graphite is soft and slippery – layers can easily slide over each other because the weak forces of attraction are easily broken. This is why graphite is used as a lubricant.

Graphite can conduct electricity – the only non-metal to do. There is a free electron from each atom to carry a charge.

How do the different properties of diamond and graphite depend on their structures?

Other allotropes of carbon Other allotropes of carbon have been discovered in the last 30 years. They are large but not really giant structures. One allotrope is buckminsterfullerene . It contains 60 carbon atoms, each of which bonds with three others by forming two single bonds and one double bond. These atoms are arranged in 12 pentagons and 20 hexagons to form spheres, which are sometimes called ‘bucky balls’. C C C C

The structure of diamond Diamond is a rare form of carbon in which each atom is covalently bonded to four others. This pattern arrangement is repeated millions of times to create a giant lattice just like in silicon dioxide C C C C C

LEARNING OBJECTIVES L6 know that living things are mainly made up from compounds containing the elements carbon, hydrogen, oxygen and nitrogen, with small amounts of other elements such as phosphorus and sulfur. be able to interpret data on percentage composition of biomolecules. remember that carbohydrates, proteins and DNA are molecular. be able to use diagrams of molecules to identify elements and molecular formulae. By the end of the lesson you should:

know that living things are mainly made up from compounds containing the elements carbon, hydrogen, oxygen and nitrogen, with small amounts of other elements such as phosphorus and sulfur.

be able to interpret data on percentage composition of biomolecules.

remember that carbohydrates, proteins and DNA are molecular.

be able to use diagrams of molecules to identify elements and molecular formulae.

Where is the biosphere?

The biosphere exists in a thin zone of air, soil, and water that is able to support life. It reaches from about 10 km into the atmosphere down to the bottom of the deepest oceans. hydrosphere biosphere lithosphere atmosphere lithosphere biosphere

The biosphere exists in a thin zone of air, soil, and water that is able to support life.

It reaches from about 10 km into the atmosphere down to the bottom of the deepest oceans.

Life in the biosphere depends on energy from the Sun and the cycling of important chemicals between different spheres.

You will remember that the lithosphere contains some 92 elements, about 47% being O. C, H, and N together amount to less than 1%.

Living things, however, are made up of only around 25 elements of which approximately 99% are C, H, N, and O.

The percentage of different elements in living tissue and in the lithosphere

These elements form the various types of chemical compounds which make up the human body: proteins vitamins fats carbohydrates minerals

proteins

vitamins

fats

carbohydrates

minerals

A small proportion of these elements are present as ionic compounds such as sodium chloride, which is dissolved in our urine and in our blood plasma . . .

. . . and calcium phosphate, which forms part of our bone structure.

vitamin A However, most of the C, H, N, and O is present in the form of large covalent molecules built mainly around chains of carbon atoms.

Molecules based around carbon atoms are called organic compounds. It is the ability of carbon to form four strong covalent bonds which allows it to create so many different molecules.

Molecules based around carbon atoms are called organic compounds.

It is the ability of carbon to form four strong covalent bonds which allows it to create so many different molecules.

The number of possible molecules is increased because organic molecules with the same atoms can be arranged in different ways. For a carbon chain with 30 atoms there are over four thousand million possible structures.

The number of possible molecules is increased because organic molecules with the same atoms can be arranged in different ways.

For a carbon chain with 30 atoms there are over four thousand million possible structures.

This explains why the biosphere contains such a large variety of biological molecules. hydrosphere biosphere lithosphere biosphere lithosphere atmosphere

Enzymes are proteins. The enzyme lysozyme catalyses the breakdown of cell walls of bacteria and helps to protect us from infection.

The angles between the bonds that hold the atoms together in DNA result in its double helix shape.

Chemical reactions in living things mean that elements such as oxygen, carbon and nitrogen cycle between the biosphere, atmosphere, hydrosphere, and lithosphere.