If a helium atom was the size of a full stop, then the average gerbil would be the size of the Earth.

Atoms: very small

Now let’s pretend that the helium atom on the right is the size of the Earth.

What’s wrong with this simple picture?

Atoms: very small

The helium atom is not in the right proportions. The three subatomic particles are wrongly enormous in comparison to the atom’s radius.

If it was the size of the Earth, then the nucleus would be about size of IVC (at the centre of the Earth).

How big is a nucleus?

Subatomic particle

Relative charge

Relative mass

Common depiction

Proton +1 1

Neutron 0 1

Electron -1 1 × 10-5

+

-

Subatomic particles in more detail

Columns of elements

H

Li

Na

K

Rb

Cs

Fr

Be

Mg

Ca

Sr

Ba

Ra

Ga

In

Tl

Al

B

Ge

Sn

Pb

Si

C

Sb

Bi

P

N

As Se

Te

Po

O

S

He

Kr

Ne

Ar

Rn

Xe

Sc Ti V Cr Mn Fe Co Ni Cu Zn

Y Zr Nb Mo Tc Ru Pd Ag CdRh

Hf Ta W Re Os Ir Au HgLa Pt

Rf Db Sg Bh Hs Mt ? ?Ac ?

Br

At

Cl

F

I

What are columns of elements called?

765432

GroupsGroups

1 0Group number

transition metals

Rows of elements

H He

Li Be N O F NeB C

Na Mg Al P S Cl ArSi

K Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge Se BrCa KrAs

Rb Y Zr Nb Mo Tc Ru Pd Ag Cd In Sn SbSr TeRh I Xe

Cs Ba Hf Ta W Re Os Ir Au Hg Tl Pb Bi PoLa AtPt Rn

Fr Ra Rf Db Sg Bh Hs Mt ? ?Ac ?

PeriodsPeriodsWhat are rows of elements called?

1

2

3

4

5

67

Period number

Going across a period, the atomic number (number of protons) increases by 1 with every element. For example, phosphorus has the atomic number 15. What is the atomic number of scandium?

Li7

3

(No. of protons)

No. of protons + neutrons

Lithium

Number of protons

Number of electrons=

Atomic number does not always equal the number of neutrons.

Lithium

Electrons 3

Protons 3

Neutrons 4

Mass number

Atomic number or proton number

Two important groups

H

Li

Na

K

Rb

Cs

Fr

Be

Mg

Ca

Sr

Ba

Ra

Ga

In

Tl

Al

B

Ge

Sn

Pb

Si

C

Sb

Bi

P

N

As Se

Te

Po

O

S

He

Kr

Ne

Ar

Rn

Xe

Sc Ti V Cr Mn Fe Co Ni Cu Zn

Y Zr Nb Mo Tc Ru Pd Ag CdRh

Hf Ta W Re Os Ir Au HgLa Pt

Rf Db Sg Bh Hs Mt ? ?Ac ?

Br

At

Cl

F

I

72

Alkali metals Halogens

Electronic Structure

• All the Group 1 elements have 1 electron in the outermost shell.

Li

Na

K

Rb

Cs

Lithium

Sodium

Potassium

Rubidium

Caesium

2,8,1

2,8,8,1

2,1

Trends in Density

Lithium, sodium and potassium are all less dense than water and so will float.

Densities follow a general, although not perfect, trend.

Element Symbol Density

Lithium Li 0.53

Sodium Na 0.97

Potassium K 0.86

Rubidium Rb 1.53

Caesium Cs 1.88

Melting Points

The atoms in the Group 1 elements are bonded together using just one outer shell electron per atom.

As a result, melting points are low compared to most metals.

Element Melt. Point (C)

Lithium 181

Sodium 98

Potassium

Rubidium 39

Caesium

Can you predict the missing data?

63

29

The Halogens

Electronic Structure

All the Group 7 elements have 7 electrons in the outermost shell.

F

Cl

Br

I

At

Bromine

Iodine

Astatine

Fluorine 2,7

Chlorine

2,8,7

And so on

Halogen molecules

All the Group 7 elements are molecules containing two atoms. Each atom is 1 electron short of full outer shell.

By sharing electrons, full outer electron shells are achieved.

F FF F

F atom F atom F2 molecule

Q: Hydrogen is not a halogen, but it could be. Explain why and draw a hydrogen molecule.

The group 7 elements get darker as you go down the group.They also get denser.

F

Cl

Br

I

Dark

er & D

enser

Bromine solution.

Note the bromine vapour above the liquid

What colour would you expect astatine to be?

The Halogens

Patterns: physical state

Melting Points and boiling points increase as the molecules get bigger.

What is the physical state: solid, liquid or gas?

Element SizeMelting

Point (oC)Boiling

Point (oC)Physical

State

Fluorine -220 -188Chlorine -101 -35Bromine -7 59Iodine +114 184

gas

gas

liquid

solid

Fill in the tableSpecies Name Protons Neutrons Electrons Electron

configuration

K Potassium 19 20 2,8,8,1

Ca

Oxygen ion 8

Mg ion in magnesium chloride

Fluoride ion

Na

lithium ion in lithium oxide

Halogen ionin LiCl

2+

+

Fill in the tableSpecies Name Protons Neutrons Electrons Electron

configuration

K Potassium 19 20 2,8,8,1

Ca

Oxygen ion 8

Mg ion in magnesium chloride

Fluoride ion

Na

lithium ion in lithium oxide

Halogen ionin LiCl

2+

+

Fill in the tableSpecies Name Protons Neutrons Electrons Electron

configuration

K Potassium 19 20 19 2,8,8,1

Ca Calcium ion 20 20 18 2,8,8

O Oxygen ion 8 8 10 2,8

Mg Mg ion in magnesium chloride 12 12 10 2,8

F Fluoride ion 9 10 10 2,8

Na Sodium ion 11 12 10 2,8

Li lithium ion in lithium oxide

3 4 2 2

Cl Halogen ionin LiCl 17 18 18 2,8,8

2+

+

2-

-

+

-

2+

Working out ionic formulaeFor each pair of atoms, work out the formula of their compound.

1. Mg and F Mg→Mg2+ F→F- Formula = MgF2

2. Ca and S Formula =

3. Li and O Formula =

4. Be and I Formula =

5. Al and O Formula =

6. Al and Cl Formula =

7. Rb and Br Formula =

8. K and S Formula =

Working out ionic formulaeFor each pair of atoms, work out the formula of their compound.

1. Mg and F Mg→Mg2+ F→F- Formula = MgF2

2. Ca and S Ca→Ca2+ S→S2- Formula = CaS

3. Li and O Li→Li+ O→O2- Formula = Li2O

4. Be and I Be→Be2+ I→I- Formula = BeI2

5. Al and O Al→Al3+ O→O2- Formula = Al2O3

6. Al and Cl Al→Al3+ Cl→Cl-Formula = AlCl3

7. Rb and Br Rb→Rb+ Br→Br- Formula = RbBr

8. K and S K→K+ S→S2- Formula = K2S

Astatine comes below iodine in Group 7 What might its melting point be (in oC)?

A. –225 B. +82 C. +150 D. +300

-220

-101

-7

114

-300

-200

-100

0

100

200

300

Period

M.P

t (C

)

F

Cl

Br

I