This document provides an overview of basic chemistry concepts including: - Atoms are made of protons, neutrons, and electrons. Ions are formed when atoms gain or lose electrons. - Elements are substances made of only one type of atom, with carbon, hydrogen, oxygen, and nitrogen being the most important elements in living things. - Molecules are formed from chemical bonds between atoms, and compounds contain two or more different types of atoms bonded together. Covalent and ionic bonding allow atoms to combine via electron sharing or transfer.

1. 02. Basic chemistry.
Ian Anderson (2013)
Saint Ignatius College Geelong

2. Knowledge and skills.
 Distinguish between an atom, an element, a molecule,
an ion and a compound.
 List the important elements found in living organisms.
 Describe the difference between covalent and ionic
bonding.
 Explain what polar molecules are.
 Describe how hydrogen bonds may form within or
between molecules with polar covalent bonds.

3. Atoms.
 Atoms are the building
blocks of all matter.
 An atom has
 A central nucleus
composed of
 Positively charged protons.
 Uncharged (neutral)
neutrons.
 Negatively charged
electrons orbitting around
the nucleus.
 The overall charge of an
atom is neutral.

4. Ions.
 If an atom gains or loses an
electron it becomes a charged
ion.
 Loses one or more electrons
 positive ion (cation).
 Gains one or more electron
Na  Na+ + e-  negative ion (anion).
H  H + + e-  The charge of an ion means
that it will be attracted to or
O+ 2e-  O2-
will repel other ions
(important in ionic bonding).

5. Elements.
 Substances that consist of only
one type of atom.
 Of the 92 naturally occurring
elements
 Only 11 are found in organisms
in more than trace amounts.
 Four of these 11, Carbon (C),
hydrogen (H), oxygen (O) and
nitrogen (N) make up 99% of
Carbon Oxygen organisms by weight.
•6 protons •8 protons  What makes one element
•6 neutrons •8 neutrons different to another is the
•6 electrons •8 electrons number of protons its atoms
has.

6. Molecules and compounds.
 Molecules = Two or more atoms
held together by chemical
bonds.
 e.g. H2, O2, CO2, CH4
O=O
 Compound = a molecule
O2
containing two or more
different types of atoms.
 e.g. CO2, CH4, H2O
Note: All compounds are
molecules. Not all molecules are
compounds!

7. Chemical bonding.
 The atoms that make up a molecule are held together
by either
 Covalent bonds
 Ionic bonds, or
 Metallic bonding (not relevant here).
 Atoms combine with other atoms in order to become
more stable.
 Atoms are most stable when they have a full outer shell
[like the noble gases in Gp18].

8. Covalent bonding.
 Only occurs between two
non-metals.
 e.g. O2, CO2, H2O, C6H12O6
 Involves the sharing of
electrons.
Methane (CH4)  Covalent bonds are stronger
than ionic bonds (generally).

9. Ionic bonding.
 Only occurs between a metal
and a non-metal.
 e.g. NaCl, CaCl2
 Involves one atom donating an
electron (or electrons) to the
other. The two (now) ions are
held together by the
Sodium chloride electrostatic forces of attraction
(NaCl)
(one ion has a +ve charge and
the other has a –ve charge).
 Ionic bonds are easier to break
than covalent bonds (generally),
but are still strong.

10. Polar molecules.
 Sometimes in a covalent bond one
Water (H2O)
atom attracts the shared electron
more strongly than the other atom
resulting in unequal sharing of
electrons.
 Even though the overall charge of
the molecule is still neutral, there
is a slightly positive region and a
slightly negative region.
 The polarity of molecules is an
important property.
 e.g. Polarity governs the way that
many molecules cross cell
membranes.
 e.g. H2O, sugars and amino acids.

11. Hydrogen bonding.
 Resulting from the attraction of
Water (H2O) δ-
the slightly positive hydrogen
atom on one polar molecule and
the slightly negative atom
δ- (usually oxygen or nitrogen) in
δ+ δ+
another polar molecule.
 Only occurs between polar
δ+ δ+
molecules.
 Much weaker than both
covalent and ionic bonds.
 Play an important role wrt the
properties of water and the
structures of both DNA and
proteins.