THE OUTER SHELL OF AN ATOM IS CALLED
THE VALENCE SHELL, AND THE ELECTRONS
IN IT ARE CALLED THE VALENCE
ELECTRONS.
ELEMENTS IN A GIVEN GROUP HAVE THE
SAME NUMBER OF VALENCE ELECTRONS,
AND, AS A RESULT, HAVE SIMILAR
CHEMICAL PROPERTIES.
THINGS WE’VE LEARNED:
1) THE ATOMIC NUMBER IS EQUAL TO THE
NUMBER OF ELECTRONS IN A NEUTRAL
ATOM.
2) THE NUMBER OF SHELLS THE ATOM OF
AN ELEMENT CONTAINS IS EQUAL TO
THE PERIOD NUMBER.
3) FOR THE REPRESENTATIVE ELEMENTS,
THE NUMBER OF VALECNE ELECTRONS IS
THE SAME AS THE GROUP NUMBER.
4) FOR THE REPRESENTATIVE ELEMENTS,
THE NUMBER OF ELECTRONS IN THE
VALENCE SHELL INCREASES BY ONE AS
YOU PROCEED ACROSS A PERIOD.
THE REPRESENTATIVE ELEMENTS ARE COLUMNS 1, 2,
AND 13 TO 18.
THE TRANSITION ELEMENTS ARE COLUMNS 3 TO 12.
THE INNER TRANSITION ELEMENTS ARE ELEMENTS 57
TO 71 AND 89 TO 103.
9
F
19
a) What is its atomic number? Atomic mass?
b) Is it a representative, transition, or inner transition
element?
c) What period is it in, and what is its group number?
d) How many total electrons are in an atom of fluorine?
e) How many valence electrons are in it?
f) How many shells of electrons are in a fluorine atom?
g) What is its electron configuration?
h) Draw a diagram of a fluorine atom.
11
Na
23
a) What is its atomic number? Atomic mass?
b) Is it a representative, transition, or inner transition
element?
c) What period is it in, and what is its group number?
d) How many total electrons are in an atom of sodium?
e) How many valence electrons are in it?
f) How many shells of electrons are in a sodium atom?
g) What is its electron configuration?
h) Draw a diagram of a sodium atom.
13
P
31
a) What is its atomic number? Atomic mass?
b) Is it a representative, transition, or inner transition
element?
c) What period is it in, and what is its group number?
d) How many total electrons are in an atom of phosphorus?
e) How many valence electrons are in it?
f) How many shells of electrons are in a phosphorus atom?
g) What is its electron configuration?
h) Draw a diagram of a phosphorus atom.
ATOMIC RADIUS (SIZE) INCREASES AS YOU
MOVE DOWN IN A GROUP.
ATOMIC RADIUS DECREASES AS YOU MOVE
ACROSS IN A PERIOD.
AS YOU MOVE DOWN IN A GROUP, EACH
PERIOD REPRESENTS AN ADDITIONAL SHELL,
SO THE VALENCE (OUTER) ELECTRONS ARE
FURTHER FROM THE NUCLEUS AND HAVE
ADDITIONAL SHIELDING.
AS YOU MOVE ACROSS IN A PERIOD, NUCLEAR
CHARGE IS INCREASING, AND THE
ELECTRONS ARE GOING INTO THE SAME
SHELL.
Atomic radius vs. atomic number
Atomic Radius (pm)
250
K
200
Na
Li
150
Mg
Al Si
Be
100
Ca
P S Cl
B C N
O F
Ar
Ne
50
H
0
0
He
2
4
6
8
10
12
Element
14
16
18
20
IONIZATION ENERGY IS THE ENERGY
REQUIRED TO REMOVE AN ELECTRON FROM A
ATOM.
IN GENERAL, IONIZATION ENERGY
INCREASES AS YOU MOVE ACROSS A PERIOD,
AND IT DECREASES AS YOU MOVE DOWN IN
A GROUP.
AS YOU MOVE ACROSS IN A PERIOD,
ATOMIC SIZE IS DECREASING AS IS
NUCLEAR CHARGE. AS YOU MOVE DOWN IN
A GROUP, ATOMIC SIZE IS INCREASING.
Ionization energy vs. atomic number
He
Ionization energy (kJ/mol)
2500
Ne
2000
Ar
F
1500
N
H
Cl
C
Be
1000
O
P S
B
500
Mg Si
Al
Li
Ca
Na
K
0
0
2
4
6
8
10
12
Element
14
16
18
20
ELECTRON AFFINITY IS THE ENERGY
RELEASED WHEN A NEUTRAL ATOM GAINS AN
ELECTRON.
YOU CAN SORT OF THINK OF IT AS BEING
THE REVERSE OF IONIZATION ENERGY –
RATHER THAN HOW EASILY AN ATOM CAN
LOSE AN ELECTRON TO HOW EASILY AN
ATOM CAN GAIN AN ELECTRON.
AS YOU MOVE ACROSS IN A PERIOD,
ELECTRON AFFINITY INCREASES, AND AS
YOU MOVE DOWN IN A GROUP, ELECTRON
AFFINITY DECREASES.
IONIZATION ENERGY AND ELECTRON
AFFINITY RELATE TO THE KINDS OF
ELEMENTS WE DEAL WITH.
METALS ARE ELEMENTS THAT CAN EASILY
LOSE ELECTRONS IN CHEMICAL REACTIONS.
NON METALS ARE ELEMENTS THAT CAN
EASILY GAIN ELECTRONS IN CHEMICAL
REACTIONS.
THESE GIVE THE ELEMENTS CERTAIN SPECIAL
PROPERTIES.
ATOMS CAN GAIN OR LOSE ELECTRONS TO
FORM IONS – AN ATOM OR GROUP OF ATOMS
WITH A CHARGE.
IF AN ATOM LOSES AND ELECTRON(S) IT
BECOMES POSTIVELY CHARGED.
IF AN ATOM GAINS AN ELECTRON(S) IT
BECOMES NEGATIVELY CHARGED.
METALS
1.METALS TEND TO HAVE LOW IONIZATION
ENERGIES AND TEND TO FORM POSITIVE
IONS
2.HAVE A SHINY LUSTER AND MOST ARE
SILVERY
3.SOLIDS ARE MALLEABLE AND DUCTILE
4.GOOD CONDUCTORS OF HEAT AND
ELECTRICITY
NONMETALS
1.NONMETALS HAVE HIGH ELECTRON
AFFINITIES AND TEND TO GAIN
ELECTRONS TO FORM NEGATIVE IONS.
2.DO NOT HAVE A LUSTER.
3.SOLIDS ARE USUALLY BRITTLE.
4.POOR CONDUCTORS OF HEAT AND
ELECTRICITY.
NOTE THAT MOST ELEMENTS ARE METALS.