atoms some slides from www.worldofteaching.com

1. Chapter 17 The atomic nature of matter
 Matter is made up of
atoms.
 Col 1:17
 He is before all things,
and in him all things
hold together.

2. Matter & Atoms
 Atoms
 -building blocks of most matter.
 Most matter is made from only about 100
different kinds of atoms.
 Each kind of atom belongs to a different
element.
 Atoms are too small to see with visible light but
can be imaged with an electron microscope.

3.  Atoms are recyclable. Atoms in your body
have been around since long before the
solar system came into existence. They
cycle and recycle among innumerable
forms, both living and non-living.

4.  Atoms are small. There are about 10 23
atoms in a gram of water ( a thimbleful)
 10 23 is greater than the number of drops
of water in all the lakes and rivers of the
world.
 Atoms are so small that there are about
as many atoms in the air in your lungs at
any moment as there are breathfuls of air
in the atmosphere of the whole world.
 Atoms are perpetually moving. They also
migrate from one location to another.

5. HISTORY OF THE ATOM
 Democritus developed the idea of
atoms 460 BC
 he pounded up materials in his
pestle and mortar until he had
reduced them to smaller and
smaller particles which he called
ATOMA
 (greek for indivisible
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6. Atomic Models
 Early Spherical Models
 Because atoms are too small to be seen, the first
theoretical models were intellectual constructions based on
the logical methods of inductive and deductive reasoning.
The classical Greek philosopher Democritus was the first to
propose the existence of atoms in 400 B.C. He reasoned
that matter cannot be divided indefinitely and must consist
of indivisible round particles called atoms. In 1800, John
Dalton arrived at the same view of atomism by using the
experimental method to study gases and compounds. His
theory was called the solid sphere, or billiard ball, model.


7. HISTORY OF THE ATOM
1808
John Dalton
 suggested that all matter was
made up of tiny spheres that
were able to bounce around
with perfect elasticity and
called them
 ATOMS
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8. HISTORY OF THE ATOM
1898
Joseph John Thompson
 found that atoms could
sometimes eject a far smaller
negative particle which he
called an
 ELECTRON
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9. HISTORY OF THE ATOM
Thompson developed the idea that an atom was made up of
electrons scattered unevenly within an elastic sphere surrounded
by a soup of positive charge to balance the electron's charge
1904
like plums surrounded by pudding.
PLUM PUDDING
MODEL
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10.  Plum Pudding Model
 In 1904 the British physicist J.J. Thompson posited
the plum pudding, or raisin bun, model of
atomism. It was based on knowledge of the
recently discovered negatively charged
subatomic particles called electrons. Thompson's
experiments with cathode ray tubes prompted
him to theorize the existence of tiny particles inside
atoms that were fundamental parts of all atoms.
His model envisioned the negative electrons, or
plums, suspended inside a positively charged
framework, or the pudding.

11. 2.2
11

12. HISTORY OF THE ATOM
1910 Ernest Rutherford
 oversaw Geiger and Marsden carrying
out his famous experiment.
 they fired Helium nuclei at a piece of
gold foil which was only a few atoms
thick.
 they found that although most of them
passed through. About 1 in 10,000 hit
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13. 1. atoms positive charge is concentrated in the nucleus
2. proton (p) has opposite (+) charge of electron
3. mass of p is 1840 x mass of e- (1.67 x 10-24 g)
 particle velocity ~ 1.4 x 107 m/s
(~5% speed of light)
(1908 Nobel Prize in Chemistry)
2.2
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14. HISTORY OF THE ATOM
 Rutherford’s new evidence allowed him to propose a
more detailed model with a central nucleus.
 He suggested that the positive charge was all in a
central nucleus. With this holding the electrons in
place by electrical attraction
 However, this was not the end of the
story.
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15. HISTORY OF THE ATOM
Niels Bohr 1913
 studied under Rutherford at
the Victoria University in
Manchester.
 Bohr refined Rutherford's
idea by adding that the
electrons were in orbits.
Rather like planets orbiting
the sun. With each orbit only
able to contain a set number
of electrons.
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16.  Planetary Models
 From 1910 to 1911, Ernest Rutherford proposed
the planetary, or nuclear, model of the atom.
He believed that atoms were composed
mostly of empty space, with a dense nucleus.
His experiments involved shooting alpha
particles at gold foil. He concluded that the
positive nucleus contains most of the atom's
mass. With his orbit model, Niels Bohr refined
the idea of the atom as a tiny solar system in
1913. Bohr's model had electrons orbiting the
nucleus in shell-like layers.

17. Bohr’s Atom
electrons in orbits
nucleus
17

18.  Electron Cloud Model
 Louis de Broglie and Erwin Schrodinger
developed the electron cloud, or quantum
mechanical, model. They based the model
on the breakthroughs of the quantum
mechanics branch of physics. Instead of
electrons in fixed orbits, the cloud model has
the orbits defined by a probability distribution
around the nucleus. Depending on their
observation and measurement, the electrons
could be in many different places, sometimes
simultaneously.

19. Evidence for atoms
 1. Brownian motion-
 pollen grains were in a constant
state of agitation, according to
Robert Brown; 1827; result from
the motion of neighboring atoms
and molecules
 2. 1970 first image of clearly
distinguishable atoms taken with
a very thin electron beam in a
scanning electron microscope.
 3. mid 1980’s- individual atoms
can be seen in the handheld
scanning tunneling microscope

20.  Element
 -made up of atoms of the same kind
 115 elements are known to date, 90 occur
in nature
 More than 99% of the material on Earth is
formed from only about a dozen of the
elements. The majority of elements are
relatively rare.

21.  5 elements in living things: O, C, H, N and
Ca
 Lightest element-
 hydrogen

22.  Atoms combine to form larger particles
called
 Molecules
 Ex. Two atoms of hydrogen (H) combine
with a single atom of oxygen(O) to form
water molecule.

23.  Compound
 -is a substance made of different elements
combined in a fixed proportion
 Some compounds are made of molecules,
 which are particles made of atoms joined
together.
 Other compounds are made of different kinds of
atoms arranged in regular pattern
 Chemical formula
 - of the compound tells the proportions of each
kind of atom.
 Ex carbon dioxide: CO2: For every carbon ( C0
atom there are two oxygen (O) atoms.

24. The Spacious Atom
 Microcosms of our
solar system, atoms
are dominantly
empty space:
 If an oxygen atom
had a total radius of
100 km, the nucleus
would be a ~1 m
diameter sphere in
the middle.

25. Electrons in Orbit
 In a simplistic model, electrons
float around the nucleus in
orbits that are sometimes
called shells.
 As the number of electrons
increases, they start to fill orbits
farther out from the nucleus.
 In most cases, electrons are
lost or gained only from the
outermost orbits.

26. The Stuff That Makes up Atoms
 Although one can subdivide atoms into
numerous subatomic particles, we will be
concerned only with protons, neutrons and
electrons
 Protons and neutrons are together in the
nucleus of an atom, whereas electrons are in
motion in orbits around the central nucleus.

27.  Protons
 - carry a positive electrical charge,
 electrons
 -carry a negative charge, and
 neutrons
 -carry no charge.
 Most atoms are electrically neutral, meaning
that they have an equal number of protons
and electrons.

28.  The atom is mostly empty
space. Its mass is almost
entirely in its
 nucleus.
 The nucleus is made of
protons and neutrons.
 The number of protons,
 the atomic number,
determines the element
to which the atom
belongs.

29.  An electrically neutral atom has electrons
outside the nucleus equal in number to
the protons inside the nucleus.
 The shell model of the atom
 -pictures electrons in spherical shells
around the nucleus.

30. Atomic Weight: It’s all in the Nucleus
 Since electrons weigh virtually nothing, the mass
of an atom is concentrated in its nucleus.
 Each atom can be described by its atomic weight
(or mass),
 which is the sum of the protons and neutrons.
 lithium:
 atomic number = 3
 3 protons
 4 neutrons
 atomic weight = 3 + 4 = 7

31. Size of Nuclei
 The number of
neutrons tends to
closely follow the
number of protons.
Atoms with more of
each are bigger and
heavier.
 A uranium atom, with
92 protons and ~146
neutrons is gigantic
compared to dinky
helium (2 + 2).

32. Maintaining
Neutrality  Most atoms are
electrically neutral,
meaning that they have
an equal number of
protons and electrons.
 A schematic model of a
lithium (Li) atom in the
ground state.
 It has 3 protons in the
nucleus, and 3
electrons in orbit.

33. Charged
Atoms: Ions
 Left to their own devices, atoms are electrically neutral. That
means that they have an equal number of protons and
electrons.
 During the course of most natural events, protons are not
gained or lost, but electrons may be.
 Atoms with more or fewer electrons than protons are
electrically charged. They are called
ions:
 An atom that loses electrons takes on a positive charge
 (cation);
 An atom that gains electrons takes on a negative charge
 (anion).

34. Electronic and Nuclear Properties
Properties of atoms reflect some combination of features
related to electrons or to the nucleus.
The electronic properties are those related to how atoms
connect to one another: bonding.
The nuclear properties include features like radioactivity.

35. Atomic Number
We distinguish one element from another on the basis of the
atomic number, which is the number of protons.
So, an atom of any element can have a variable number of
electrons and neutrons, but given the number of protons, the
fundamental properties of the element are unchanged.
This is the basis for Dmitri Mendeleev’s
organization of the
Periodic Table of the Elements.
The table is a way of organizing elements
on physical grounds,
but also serves to group elements with
consistent chemical properties.

36.  The periodic table
 is a chart of elements arranged
according to atomic structure and
properties.
 Elements in the same column have similar
chemical properties, reacting with other
elements in similar ways to form new
compounds and materials because their
outermost electrons are arranged in a
similar fashion, they belong to the same
 group of elements

37. The Periodic Table
The periodic table is read from top to bottom, left to right, as
atomic number increases: 1=H, 2=He, 3=Li, 4=Be, 5=B, 6=C,
and so on.

38. Elements in columns (groups)
have similar
outer-electron configurations,
and so tend to behave similarly.
The Periodic Table
alkali
earths
rare
earths
halogens
noble gases
transition metals
actinides

39. The Periodic Table: the Bulk Earth
A small number of elements make up >99% of the solid Earth.
O = oxygen
Na = sodium
Mg = magnesium
Al = aluminum
Si = silicon
S = sulfur
Ca = calcium
Fe = iron
Ni = nickel

40. The Periodic Table: the Crust
The crust is a little more elementally interesting (again, as
a result of differentiation), but it is still mainly made of a
small number of elements.
C = carbon
P = phosphorus
K = potassium
Ti = titanium
Mn = manganese

41.  BUT... although each
element has a defined
number of protons, the
number of neutrons is
not fixed.
 Atoms of the same
element, with the same
atomic number, having
different numbers of
neutrons are called
 Isotopes of that
element.

42. Isotopes
Carbon (atomic # 6) has three natural isotopes
with atomic weights of 12, 13 and 14.
isotope #p #n
====== == ==
C-12 6 6
C-13 6 7
C-14 6 8
Tin (Sn, atomic # 50) has ten natural isotopes with
atomic masses of 112, 114, 115, 116, 117, 118, 119,
120, 122 and 124. How many protons and neutrons
do these isotopes have?