Download Atomic Structure

Atomic Structure
called
“nucleons”
Name
Protons
Neutrons
Electrons
Mass
1
1
1/1837
Charge
+1
0
-1
Location
Nucleus
Nucleus
Orbit nucleus in outer shells
The number of protons equals the atomic number. This is the number which defines the
element (i.e. all elements have different atomic numbers). The atomic number can be
written as a subscript (below the line) in front of the symbol (e.g. 6C).
In a neutral atom, the number of electrons equals the number of protons.
The mass number is equal to the number of nucleons. The mass number can be written as a
superscript before the symbol (e.g. 12C).
Isotopes are when a single element has atoms with the same number of protons, but
different number of neutrons (and therefore mass number).
Example:
Chlorine comes in two different forms. One form has a mass number of 35
and the other has a mass number of 37:
35
Cl
17 protons
18 neutrons
37
Cl
17 protons
20 neutrons
Relative atomic mass (Ar) – this is the mass of an “average” atom of an element divided by
one atom of 1H. The Ar takes into account the relative abundance of the naturally occurring
isotopes of the element….ok, so basically, you find the average of the masses of the
different isotopes! The mass number is always an integer (that’s a “whole number” for all
you non-mathematicians) BUT the Ar does not have to be.
Example:
What is the Ar of chlorine given that there are two isotopes: 35Cl (which is 75% abundant) and 37Cl
(which is 25% abundant)?
To do this, we need to look at the abundance to work out the mass of an “average atom” of
Cl. As 35Cl is 75% abundant, we multiply 35 by 75% (i.e. 0.75) and as 37Cl is 25%
abundant, we multiply 37 by 25% (i.e. 0.25). The two numbers are then added together and
divided by the mass of one atom of 1H (i.e. 1 – so this step is pointless…):
(35 × 0.75) + (37 × 0.25) = 35.5
(If you didn’t understand that…don’t worry, here’s an easier way…just for you…simply
remember this formula:
the sum of: mass × abundance (for all the isotopes)
The Periodic Table
There are approximately 100 elements. Everything is made up of one or more elements. The
periodic table shows elements in increasing atomic number.
Electrons are accommodated in shells. The maximum in the first shell is 2, the maximum in
the second shell is 8 and the maximum in the third shell is also 8. Electrons always fill
lower energy shells (i.e. closer to the nucleus) first.
..
.
1st electron shell (can hold up
to 2 electrons)
..
..
.
..
The first 20 elements:
Atomic
Symbol
Number
1
H
2
He
3
Li
4
Be
5
B
6
C
7
N
8
O
9
F
10
Ne
11
Na
12
Mg
13
Al
14
Si
15
P
16
S
17
Cl
18
Ar
19
K
20
Ca
2nd electron shell (can hold up
to 8 electrons)
nucleus – with protons and neutrons
Element
Shell 1
Shell 2
Shell 3
Shell 4
Hydrogen
Helium
Lithium
Berillium
Boron
Carbon
Nitrogen
Oxygen
Fluorine
Neon
Sodium
Magnesium
Aluminium
Silicon
Phosphorous
Sulphur
Chlorine
Argon
Potassium
Calcium
1
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
1
2
3
4
5
6
7
8
8
8
8
8
8
8
8
8
8
8
1
2
3
4
5
6
7
8
8
8
1
2
Other important elements include:
Atomic
Symbol Element
number
26
Fe
Iron
29
Cu
Copper
30
Zn
Zinc
35
Br
Bromine
Atomic
number
47
53
56
82
Symbol
Element
Ag
I
Ba
Pb
Silver
Iodine
Barium
Lead
In the periodic table, elements are arranged in rows named periods when a single electron
shell is filling. We start a new period when we start filling the next electron shell.
At the top of each column or group, there is a number showing how many electrons are in
the outer shell (e.g. group 7 has 7 electrons in the outer shell).
Element
An element is a pure substance which cannot be broken down any simpler by chemical
means. Atoms of the same element have the same atomic number. A sample of an element
may be made up of atoms or molecules.
Compound
Compounds are pure substances containing two or more elements chemically bonded
together in fixed proportions by mass.
Example:
H2O
2g Hydrogen,
16g oxygen
1g Hydrogen,
8g oxygen
The properties of a compound are different to those of its constituent element. The chemical
bonds in compounds are either ionic or covalent (we will look at this a bit later…fun fun
fun!). Compounds can be either ions or molecules.
Mixtures
Vary in composition and can be physically separated.
Mixtures and Compounds – the difference!
Iron and sulphur mixed together looks like yellow powder with grey bits in it…(a mixture)
You can separate then by:
using a magnet (the smart way of getting a needle from a haystack!)
-
dissolving the sulphur in a solvent (e.g. toluene) and filtering when hot. Then
let the solution cool and the sulphur crystallises.
If the mixture is heated, an exothermic reaction (a reaction that gives out heat) takes place.
There are 3 things to prove that a reaction has taken place:
1.
It continues to glow red hot even when you stop heating it
2.
The product is a brittle grey solid, which does not look like the mixture
3.
The mixture reacts with dilute hydrochloric acid to produce hydrogen whereas
the compound (after heating) reacts with hydrochloric acid to make foul
smelling hydrogen sulphide.
Iron(s) +
Fe(s) +
Sulphur (l)
S(l)
→
→
Iron (II) Sulphide(s)
FeS(s)
Atoms of different elements can combine to form compounds by the formation of new
chemical bonds.
Oxygen(g)
→
Magnesium Oxide(s)
Magnesium(s) +
2Mg(s)
+
O2 (g)
→
2MgO(s)
Ions
Ions are formed from atoms by the gain or loss of electrons. The nucleus is left unaffected.
The maximum that can be lost or gained is 3. Generally we form an ion which has a noble
gas configuration (i.e. all full outer shells).
Positive ions are called cations.
Negative ions are called anions.
Atoms of elements in group 1 LOSE one electron to form a 1+ ion of noble gas
configuration:
Na → Na+ + 1e– (electron)
2, 8, 1
2, 8 (same electron configuration as neon)
Atoms of elements in group 2 LOSE two electrons to form a 2+ ion of noble gas
configuration:
Ca → Ca2+ + 2e– (electrons)
2, 8, 8, 2
2, 8 (same electron configuration as argon)
Atoms of elements in group 3 LOSE three electrons to form a 3+ ion of noble gas
configuration:
Al → Al3+ + 3e– (electrons)
2, 8, 3
2, 8 (same electron configuration as neon)
Atoms of elements in group 7 GAIN one electron to form a 1– ion of noble gas
configuration:
(electron) e– + Cl → Cl–
2, 8, 7
2, 8, 8 (same electron configuration as argon)
Atoms of elements in group 6 GAIN two electrons to form a 2– ion of noble gas
configuration:
(electrons) 2e– + O → O2–
2, 6
2, 8 (same electron configuration as neon)
Formulae of Ionic compounds
The ones in red / green need to be learnt, the rest can be worked out by looking at their
position in the periodic table.
2–
1–
1+
O2– (oxygen)
F– (fluoride)
Li+ (lithium)
S2– (sulphide)
Cl– (chloride)
Br– (bromide)
I– (iodide)
Na+ (sodium)
K+ (potassium)
Ag+ (silver)
H+ (hydrogen)
Cu+ (copper I)
SO42– (sulphate)
CO32– (carbonate)
SO32– (sulphite)
OH– (hydroxide)
NO3– (nitrate)
HCO3–
(hydrogencarbonate)
CH3CO2– (ethanoate)
NH4+
(ammonium)
2+
Mg2+
(magnesium)
Ca2+ (calcium)
Ba2+ (barium)
Zn2+ (zinc)
Pb2+ (lead)
Cu2+ (copper II)
Fe2+ (iron II)
3+
Al3+ (aluminium III)
Fe3+ (iron III)
Radical Ions (2 or more atoms
covalently bonded together carrying a
charge. they behave as a single unit)
Both copper and iron can form ions of more than one charge. We have to write the charge in
roman numerals in the name to distinguish between the compounds.
Copper (I) oxide
Cu2O =
CuO =
Copper (II) oxide
FeCl2 =
FeCl3 =
Iron (II) chloride
Iron (III) chloride
Learning how to write formulae is VERY important…lots of chemistry is about formulae...
Basically, all you have to do is take the symbol of each element and put it together making
sure that the charges cancel out and that you put the positive ion first.
So…three steps:
1.
In name and formulae, the positive ion goes first
2.
The total charge must equal 0
3.
If you have to multiply a radical ion, put it in brackets
Examples:
Sodium Chloride (Na+ and Cl–)
→
NaCl
Calcium Chloride (Ca2+ and Cl–) →
CaCl2
Calcium Nitrate (Ca2+ and NO3–) →
Ca(NO3)2
(notice that 2 Cls are needed to cancel the 2+ of the Ca)
Try some for yourself (just to see if you really understood it and aren’t just pretending to):
1.
2.
3.
4.
Sodium sulphate
Aluminium chloride
Calcium sulphide
Aluminium nitrate
5.
6.
7.
8.
Sodium nitrate
Ammonium chloride
Ammonium sulphide
Aluminium sulphide
A GCSE Chemistry word-fill worksheet on
"ATOMIC STRUCTURE, ISOTOPES and ELECTRON STRUCTURE"
15
2
2
2.7
2.8.5 21 21 22 26 26 2nd 3 30 4th 5 5th 7 8 8 9
atomic electrons electrons electrons group iron isotopes
mass neutrons neutrons nucleus number period shell shells three
mass
Q1(a) Atoms are made of
(+),
(0) and
fundamental particles called protons
(-). (b) The centre of the atom is called
the
. (c) It consists of protons and
of the mass of the atom.
and contains most
Q2(a) The number of protons in the atom is called the
number. It also equals the number of
atom. (b) The
the nucleus.
in a neutral
is the sum of the protons and neutrons in
Q3 An atom of mass number 43, and atomic number 21, consists of
protons,
neutrons and
electrons.
Q4 (a) In the symbol for an atom of
the atom consists of
protons,
shown on the left,
neutrons and
electrons. (b) Atoms of the same element with a different
number due to different numbers of neutrons are called
.
Q5(a) Electrons are arranged around the nucleus in energy levels or
. (b) The 1st shell can have a maximum of
shell a maximum of
of
electrons, the
electrons and the 3rd shell a maximum
electrons. (c) The 19th and 20th electrons go in the
shell. (d) The electron arrangement, showing the number of
electrons in each
can be written out in shorthand eg 2.8.6 for
the 1st, 2nd and 3rd shells respectively.
atomic
Q6(a) Apart from hydrogen and helium in period 1 of the Periodic
Table the last number in the arrangement is equal to the
number in the Periodic Table. (b) The number of shells used
containing electrons is equal to the
number. (c) The number
of electrons in an atom is equal to the
or proton number.
Q7(a) Phosphorus has an atomic number of 15 so the atoms have
protons or 15
. (b) The electron arrangement will be
. (c) In the Periodic Table it will be a member of Group
and it will be the
element along Period
Q8(a) Fluorine has an atomic number of
.
so the atoms have 9
protons or electrons. (b) Its electron arrangement is
belongs to Group
on Period
.
and it
Ionic Equations – Questions (A) Translate into symbols and balance each equation: 1. calcium carbonate breaks down on heating to give calcium oxide and carbon dioxide. 2. sulphur burns in oxygen to form sulphur dioxide gas. 3. heating magnesium and sulphur powders together produces solid magnesium sulphide. 4. sodium hydroxide and hydrochloric acid react to form sodium chloride and water. 5. hydrogen gas and oxygen gas burn together to form water. 6. zinc metal and copper sulphate solution react to produce copper and zinc sulphate solution. (B) Balance these equations and add state symbols: 1. CuO + HNO3 to Cu(NO3)2 + H2O 2. Al + Cl2 to AlCl3 3. N2 + H2 to NH3 4. Na + H2O to NaOH + H2 5. K2CO3 + H2SO4 to K2SO4 + H2O + CO2 6. Fe + H2SO4 to FeSO4 + H2 7. CH4 + O2 to CO2 + H2O 8. Pb(NO3)2 + NaCl to PbCl2 + NaNO3 (C) Balance these equations: 1. MnO2 + HCl to MnCl2 + Cl2 + H2O 2. HBr + H2SO4 to SO2 + Br2 + H2O to I2 + H2S + H2O to KCl + MnCL2 + Cl2 + H2O 3. HI + H2SO4 4. KMnO4 + HCl 5. FeSO4 + KMnO4 + H2SO4 to (Fe)2 (SO4)3+K2SO4+MnSO4+H2O Equation Answers
A.
1.
2.
3.
4.
5.
6.
.
CaCO3(s)
S(s) + O2(g)
Mg(s) + S(s)
NaOH(aq) + HCl(aq)
2H2(g) + O2(g)
Zn(s) + CuSO4(aq)
CaO(s) + CO2(g)
SO2(g)
MgS(s)
NaCl(aq) + H2O(l)
2H2O(l)
ZnSO4(aq) + Cu(s)
B.
1.
2.
3.
4.
5.
6.
7.
8.
CuO(s) + 2HNO3(aq)
2Al(s) + 3Cl2(g)
N2(g) + 3H2(g)
2Na(s) + 2H2O(l)
K2CO3(s) + H2SO4(aq)
Fe(s) + H2SO4(aq)
CH4(g) + 2O2(g)
Pb(NO3)2(aq) + 2NaCl(aq)
Cu(NO3)2(aq) + H2O(l)
2AlCl3(s)
2NH3(g)
2NaOH(aq) + H2(g)
K2SO4(aq) + H2O(l) + CO2(g)
FeSO4(aq) + H2(g)
CO2(g) + 2H2O(g)
PbCl2(s) + 2NaNO3(aq)
C.
1.
2.
3.
4.
MnO2 + 4HCl
2HBr + H2SO4
8HI + H2SO4
2KMnO4 + 16HCl
10FeSO4 + 2KMnO4 +
5.
8H2SO4
MnCl2 + Cl2 + 2H2O
SO2 + Br2 + 2H2O
4I2 + H2S + 4H2O
2KCl + 2MnCl2 + 5Cl2 + 8H2O
5(Fe)2(SO4)3 + K2SO4 + 2MnSO4 +
8H2O