Atoms

Question 1

Define proton number (atomic number)…

Answer 1

● The number of protons in the nucleus of an atom

Question 2

Define nucleon number (mass number)…

Answer 2

● The total number of protons and neutrons in the nucleus of an atom

Question 3

Use proton number and the simple structure of atoms to explain the basis of
the Periodic Table with special reference to the elements of proton number
1 to 20

Answer 3

● Elements are arranged in order of atomic (proton) number (bottom number) and
so that elements with similar properties are in columns, known as groups.
● Elements in the same periodic group have the same amount of electrons in their
outer shell, which gives them similar chemical properties.
● Elements are arranged in order of increasing atomic number, in rows called
periods and elements, with similar properties are placed in the same vertical
columns called groups

Question 4

Define isotopes…
● Atoms of the same element which have the same proton number but a different
nucleon number (different number of neutrons)

Question 5

(Extended only) Understand that isotopes have the same properties because
they have the same number of electrons in their outer shell

Answer 5

● Isotopes have the same chemical properties because they have the same
number of electrons in their outer shell and the number of electrons in the outer
shell is responsible for chemical reactions
● they also have the same number of protons so are still classed as the same
element

Question 6

State the two types of isotopes as being…

Answer 6

● Radioactive and non-radioactive

Question 7

State one medical and one industrial use of radioactive isotopes

Answer 7

● Medical uses:
o Sterilising equipment
o Tracers
● Industrial uses:
o Smoke alarms
o Tracers

Question 8

Describe the build-up of electrons in ‘shells’ and understand the significance
of the noble gas electronic structures and of the outer shell electrons (The
ideas of the distribution of electrons in s and p orbitals and in d block
elements are not required.) Note: a copy of the Periodic Table, will be
available in Papers 1, 2, 3 and 4.

Answer 8

● Electrons are arranged around the nucleus in shells. Starting with the first shell
(closest to the nucleus), each shell is filled with electrons before any further
shells gain any electrons
o First shell can have up to 2 electrons
o Second shell can have up to 8 electrons
o Third shell can have up to 8 electrons
● When reacting, all atoms will try to acquire this perfect arrangement of electrons
– i.e. having the maximum number of electrons as possible in their outer shell –
therefore, all atoms try to have 8 electrons in their outer shell (unless they only
have one shell then they will try to have only 2) because this is the most stable
arrangement
● Nobles gases have 8 electrons in their outer shells
already (except helium, which has 2), making them
very stable so unreactive

Question 9

Describe the differences between elements, mixtures and compounds, and
between metals and non-metals

Answer 9

Element = substance made from only one type of atom
● Compound = substance made from two or more elements that have reacted
chemically with each other
● A mixture:
o Consists of 2 or more elements or compounds not chemically combined
together
o Chemical properties of each substance in the mixture are unchanged
● Metals = elements that react to form positive ions.
o Majority of elements are metals.
o Found to the left and towards the bottom of the periodic table., they lose
electron(s) in order to form these positive ions
● Non-metals = elements that do not form positive ions.
o Found towards the right and top of the periodic table, because they gain
electron(s) in order to form these negative ions
● Metals are generally conductive
● Non metals (excluding graphite) are generally not conductive

Question 10

Describe an alloy, such as brass, as a mixture of a metal with other elements

Answer 10

● Most metals in everyday uses are alloys. Pure copper, gold, iron and aluminium
are all too soft for everyday uses and so are mixed with small amounts of other
elements (in these cases with similar metals) to make them harder for everyday
use.
o Gold in jewellery is usually an alloy with silver, copper and zinc
o brass is an alloy of copper and zinc
● alloys are harder than pure metals because:
o in a pure metal, all the + ions are the same size
and in a regular arrangement so can easily slide
over each other
o in an alloy, there are + ions from different
metals, meaning they are different sizes, which
disrupts the regular arrangement and prevents
the layers from sliding as easily

Question 11

Describe the formation of ions by electron loss or gain

Answer 11

● an ion is an atom or group of atoms with a positive or negative charge
● ions are formed by an atom losing or gaining electrons (which have a -1 charge)
● if an atom gains electrons, it becomes a negative ion
● if an atom loses electrons, it becomes a positive ion
o Cation = positive ion (+ -> ca+ion)
o Anion = negative ion (Negative -> aNion)

Question 12

Describe the formation of ionic bonds between elements from Groups I and
VII

Answer 12

● an ionic bond is formed when an electron is transferred from one atom to
another
● when ionic bonds are formed between group 1 and 7:
o group 1 atom loses one electron and forms a +1 ion
o group 7 atom gains the electron the group 1 atom lost and becomes a -1
ion
● Electron transfer during the formation of an ionic compound can be represented
by a dot and cross diagram (see eg for NaCl below):

Question 13

(Extended only) Describe the formation of ionic bonds between metallic and
non-metallic elements

Answer 13

● Metal + Non-metal: electrons in the outer shell of the metal atom are
transferred
o Metal atoms lose electrons to become positively charged ions
o Non-metal atoms gain electrons to become negatively charged ions

Question 14

(Extended only) Describe the lattice structure of ionic compounds as a
regular arrangement of alternative positive and negative ions

Answer 14

● Held together by strong electrostatic forces of attraction between oppositely
charged ions, which are regularly arranged
● The forces act in all directions in the lattice, and this is called ionic bonding.
Strong electrostatic forces of attraction between alternating positive and
negative ions
● Requires a lot of energy to overcome these forces of attraction

Question 15

Describe the formation of single covalent bonds in H2
, Cl2
, H2O, CH4
, NH3 and
HCl as…

Answer 15

● The sharing of pairs of electrons leading to the noble gas configuration
● all of these compounds have single covalent bonds e.g. water (H2O):

Question 16

Describe the differences in volatility, solubility and electrical conductivity
between ionic and covalent compounds

Answer 16

● Volatility (ease of evaporation):
○ Covalent compounds: giant covalent structures have high melting/boiling
points and so low volatility. Simple molecular covalent substances have
low melting/boiling points so have high volatility
○ Ionic compounds: compounds have high melting and boiling points (low
volatility)
● Solubility:
○ Ionic substances
■ Tend to be soluble in water, but insoluble in other covalently
bonded solvents e.g. ethanol or propanone
○ Covalent substances
■ Opposite of ionic substances in terms of solubility
■ Soluble in covalent type solvents
■ Insoluble in water
● Electrical conductivity:
o Covalent compounds do not conduct electricity – they have no free
flowing particles able to carry charge (except for graphite)
o Ionic compounds conduct electricity ONLY when molten or dissolved in
aqueous solution, because then the ions are able to move and carry
charge, conducting electricity - when solid, the ions are fixed

Question 17

(Extended only) Explain the differences in melting point and boiling point of
ionic and covalent compounds in terms of attractive forces

Answer 17

○ Covalent compounds:
■ Substances that consist of giant covalent structures are solids with very
high melting points. All of the atoms in these structures are linked to
other atoms by strong covalent bonds, which must be overcome to melt
or boil these substances.
■ Substances that consist of small molecules are usually gases or liquids
that have low boiling and melting points.They have weak intermolecular
forces between the molecules. These are broken in boiling or melting, not
the covalent bonds.
○ Ionic compounds:
■ Strong electrostatic forces of attraction between oppositely charged ions
■ Requires a lot of energy to overcome these forces of attraction
■ Therefore, the compounds have high melting and boiling points

Question 18

Describe the giant covalent structures of graphite and diamond
Diamond

Answer 18

● In diamond (right), each carbon is joined to 4 other carbons
covalently.
o It’s very hard, has a very high melting point and does not
conduct electricity.
Graphite
● In graphite, each carbon is covalently bonded to 3 other carbons, forming layers
of hexagonal rings, which have no covalent bonds between the layers.
o The layers can slide over each other due to no covalent bonds between
the layers, but weak intermolecular forces. Meaning that graphite is soft
and slippery.
● One electron from each carbon atom is delocalised.
o This makes graphite similar to metals, because of its delocalised
electrons.
o It can conduct electricity – unlike Diamond

Question 19

(Extended only) Describe the macromolecular structure of silicon(IV) oxide
(silicon dioxide)

Answer 19

● Each silicon atom is covalently bonded to 4 oxygen atoms
● Each oxygen atom is covalently bonded to 2 silicon atoms
● Therefore, the formula is SiO2. This is the empirical formula, which is used for all
giant molecules, because there are too many atoms to give the molecular
formula

Question 20

Relate their structures to their uses, e.g. graphite as a lubricant and a
conductor, and diamond in cutting tools

Answer 20

● Graphite
o Lubricant – layers slide over each other
o Conductor – can conduct electricity
● Diamond
o Cutting tools – very hard due to rigid structure

Question 21

(Extended only) Describe the similarity in properties between diamond and
silicon(IV) oxide, related to their structures

Answer 21

● Similar properties:
o Very hard
o Very high melting and boiling points
o Insoluble in water
o Does not conduct electricity
● These are due to the strong covalent bonds that hold the atoms in a rigid
structure

Question 22

(Extended only) Describe metallic bonding as a lattice of positive ions in a
‘sea of electrons’ and use this to describe the electrical conductivity and
malleability of metals

Answer 22

● metallic bonding: a regular lattice of + metal ions surrounded by a sea of
delocalised electrons
● Metals consist of giant structures of atoms arranged in a regular pattern.
● The electrons in the outer shell of metal atoms are delocalised and so are free to
move through the whole structure.
● The sharing of delocalised electrons gives rise to strong metallic bonds.
electrical conductivity: metals can conduct electricity because the sea of
delocalised electrons is able to move
● malleability: the regular arrangement of equally sized metal ions means that the
layers of ions are able to slide over each other easily,without the metal
shattering, making metals malleable