• Matter is made of atoms
•Atoms are the basic building block of
matter
400 BC Democritus
THE ATOM IS AN INDIVISIBLE PARTICLE
• the atom is the smallest particle of matter
1808 Dalton
THE SOLID SPHERE MODEL
• atoms are solid , indestructible spheres (like
billiard balls)
1897 J.J. Thompson
THE RAISIN BUN MODEL
• atoms are solid spheres made up of solid
positive mass with tiny negative particles
embedded in the positive
1911 Rutherford
THE PLANETARY MODEL
• the atom is composed of a positive
nucleus and negative electrons which
surround the nucleus
• atom is mostly empty space
• Gold foil experiment
1913 Niels Bohr
• electrons orbit the nucleus in different energy
levels
• electrons can move from one level to another by
gaining or losing packets of energy
• electrons are more stable when they are closer to
the nucleus
1932 Sir James Chadwick
• the nucleus contains particles called neutrons and
positively charge protons
Consists of sub-atomic
particles:
•protons
•neutrons
•electrons
•Protons and neutrons are located in the
nucleus
•Electrons orbit the nucleus
Determining the number of subatomic
particles
Each element has an atomic number and a mass
number
Atomic number
= no. of protons
= no. of electrons
Mass number
= no. of protons + no. of neutrons
Therefore, no. of neutrons = mass number – atomic number
Example: How many protons, neutrons and
electrons does carbon have?
Atomic number = 6
Mass number = 12
Number of protons: 6
Number of neutrons: 12-6 = 6
Number of electrons: 6
mass number
A
Z
E
chemical symbol
atomic number
An international
recognized system
that allows anyone
to communicate
information about
the atom
• Electrons move around the nucleus in fixed energy
levels called shells.
•Shells close to the
nucleus are lower in
energy while shells
farther away are high in
energy.
• Shells are number
outwards from the
nucleus (1,2,3..) and are
also lettered (K,L,M,N...)
Different shells hold different numbers of electrons. The
maximum number of electrons that can fit into a shell
is 2n2 (n = shell number)
Shell number (n)
1
2
3
4
Representative letter
K
L
M
N
Maximum
number of electrons
in this shell (2n2)
2X12 =2
2X22
2X32
2X42
=8
= 18
= 32
Bohr diagram
number of protons and neutrons written in the center
•electrons drawn in circular orbits around the nucleus
10 P
10 N
Example: Chlorine
Atomic number is 17.
17 protons and electrons
Mass number is 35.
35 - 17 = 18 neutrons
17 P
18 N

Subshells are energy levels found within
shells.
There are four different types of subshells

Named- s, p, d, f .

Subshell energy: s<p<d<f

subshell
Number of
electrons
s
2
p
6
d
10
f
14

The way in which electrons are arranged
around the nucleus of an atom is called the
electron configuration of the atom.

Electrons fill shells and subshells of lowest
energy first.

Aluminum – 13 electrons
 1s22s22p63s23p1

Calcium – 20 electrons
 1s22s22p63s23p64s2

Iron – 26 electrons
 1s22s22p63s23p64s23d6

Bromine – 35 electrons
 1s22s22p63s23p64s23d104p5

Aluminum – 13 electrons

Calcium – 20 electrons

Iron – 26 electrons

Bromine – 35 electrons

Orbital is the 3 dimensional space around a
nucleus in which electrons are most likely to be
found

Each orbital can hold up to 2 electrons.
Timberlake LecturePLUS 2000
s subshell: spherical
1 orbital-2 electrons
z
x
y
p subshell: pair of lobes
3 orbital- 6electrons
d subshell: double dumpbells
5 orbital-10 electrons
x
y
xy
xz
yz
x2-y2
z2
At ground state the electron is at its lowest possible
energy level (electrons are as close to the nucleus as
possible).
Example: Sodium (Z=11)
Ground state electron configuration: 2, 8, 1
If atoms are given large amounts of energy (heat, light
or electricity), the electrons can jump to an orbit
further away from the nucleus. The atom is then in an
excited state.
Fluorine
Ground state
F: 1s2 2s2 2p5
Exited state
F*: 1s2 2s1 2p5 3s1
When the electrons return to the ground state, they
release this energy in the form of light. The light released
has a specific wavelength corresponding to the
difference between the energy levels.
Emission Spectra are emissions of light from atoms
that have been heated or provided with energy.
Emission Spectra are different for each material.
Fe
They can be used to determine the identity of an
unknown sample of an element.
Hydrogen
Helium
1) Draw 2 Bohr-Rutherford diagrams for lithium; one in
the ground state and one in the excited state. Make
sure to include the energy put into the system, and
energy released.
2) Explain why different elements have different
emission line spectrums.
Identify each of the unknown gases based on the
emission line spectrums provided. The 4 possibilities are
oxygen, hydrogen, helium and neon.
A
B
C
D