c4 revision
TRANSCRIPT
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