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Topic 2 – National Chemistry Summary Notes
Atomic Structure
Classifying Elements
Chemists have classified elements, i.e. put elements into different sets, by
arranging them in The Periodic Table. Some of the ways elements have been
classified are shown in the following tables.
Solids
Liquids
Gases
copper
Bromine
oxygen
gold
Mercury
helium
Metals
Non-metals
aluminium
chlorine
silver
nitrogen
Note: metals are found on the left of the dark line on The Periodic Table and
non-metals are found on the right
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Naturally Occurring
Made by Scientists
iron
einsteinium
sodium
mendelevium
Note: see * on The Periodic Table for the elements made by scientists
The Periodic Table
The Periodic Table is made up of rows and columns of elements.
The rows from left to right across The Periodic Table are called rows or
periods
The columns up and down are called columns or groups
Some of the groups are given a particular family name as shown in the table on
the following page.
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The Alkali Metals are very reactive.
The Noble Gases are unreactive non-metals.
The Halogens are reactive non-metals.
Group
Name
1
alkali metals
7
(contains solids, liquids and gases)
halogens
0
noble gases
see note below
transition metals
Note: The Transition Metals are the large group of metals which join the left
half of The Periodic Table to the right
All the elements in a particular group have similar chemical properties and show
trends. For example, The Alkali Metals all react with water and their reactivity
in water increases as we go down the group, i.e. the reaction becomes more
violent.
When an alkali metal reacts with water it floats on the surface of the water as
it is less dense than water.
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Problem Solving Questions
Question 1
The following table shows the state of each of The Halogens except astatine.
Predict the state of astatine.
Halogen
State
fluorine
gas
chlorine
gas
bromine
liquid
iodine
solid
fluorine gas
chlorine gas
bromine liquid
iodine solid
astatine ?
Astatine is likely to be a solid as, as we go down The Halogen group the trend
has become a solid.
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Question 2
Use The Periodic Table below to answer the following questions.
a. identify two elements in the same row
b. identify two elements in the same group
c. identify The Noble Gas
D
B
A
Transition Metals
E
C
a.
b.
c.
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The Structure of The Atom
All matter is made of atoms.
When a substance contains only one kind of atom it is known as an element. For
example, the element gold only contains gold atoms.
Atoms contain a very small nucleus with electrons moving around outside the
nucleus. Protons and neutrons are found inside the nucleus.
Subatomic Particles
As protons, neutrons and electrons collectively make up an atom they are
individually called subatomic particles. The following table gives some
information about these particles.
Subatomic
Particle
Charge Mass
Location in Atom
proton
positive
1
in nucleus
neutron
neutral
1
in nucleus
electron
negative
almost zero
outside nucleus
nucleus
(protons and neutrons)
electrons
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In an atom:
number of protons = number of electrons
Consequently, atoms are neutral (i.e. they do not have an electric charge)
because the number of positive protons equals the number of negative
electrons.
In more difficult terms, the positive charge on the nucleus is equal to the sum
of the negative charges of the electrons.
Atomic Number
The number of protons defines an element and is known as the atomic number.
atomic number = number of protons
The atoms of each different element have a different atomic number and
consequently vary in size and mass.
Element
Atomic Number Number of Protons
carbon
6
6
lead
82
82
Elements are arranged in The Periodic Table in order of increasing atomic
number.
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Mass Number
The mass number of an atom can be worked out using the following equation:
mass number = number of protons + number of neutrons
Example
Potassium has 19 protons and 20 neutrons. What is potassium’s mass number?
mass number = number of protons + number of neutrons
= 19 + 20
= 39
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In an atom:
number of protons = number of electrons
atomic number = number of protons = number of electrons
mass number = number of protons + number of neutrons
Therefore,
number of neutrons = mass number – number of protons
number of protons = mass number – number of neutrons
Summary
Using the above information, fill in the blanks in the following table.
Element Symbol Atomic
Number
Mass
Number
Number
of
Protons
Number
of
Neutrons
Number
of
Electrons
hydrogen
1
0
lithium
7
You will find the answers on the next page!
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Element Symbol Atomic
Number
Mass
Number
Number
of
Protons
Number
of
Neutrons
Number
of
Electrons
hydrogen
H
1
1
1
0
1
lithium
Li
3
7
3
4
3
mass number = number of protons + number of neutrons
7 = 3 + number of neutrons
7-3 = number of neutrons
4 = number of neutrons
Nuclide Notation
Li
number of protons = 3
number of electrons = 3
number of neutrons = 4
When an atom is shown in
this manner it is known as
nuclide notation.
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mass number
atomic number
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Isotopes are atoms with the same atomic number but with different
mass numbers.
Isotopes
For example,
Cl and
Cl are isotopes
number of protons = 17 number of protons = 17
number of electrons = 17 number of electrons = 17
number of neutrons = 18 number of neutrons = 20
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Relative Atomic Mass
Most elements exist as a mixture of isotopes.
The Relative Atomic Mass (RAM) of an element is the average mass of all the
isotopes of that element, allowing for their abundance (abundance is how much
of each isotope is naturally present)
The RAM of chlorine is 35.5 amu (atomic mass units). No chlorine atom actually
has this mass, it is just the average mass of all the chlorine atoms. As chlorine’s
Relative Atomic Mass is nearer 35 than 37 the
Cl isotope must be more
abundant, i.e. a greater proportion of
Cl exists.
Since RAM’s are averages, they are rarely a whole number.
The RAM of an element is given on page 4 of the data book.
Note: The RAM is also known as Average Atomic Mass
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Electron Arrangement
The electrons in an atom are arranged in energy levels (aka electron levels)
around the nucleus. The way they are arranged is their electron arrangement
and this is given on p.1 of the data book. For example,
Sodium 2, 8, 1
first second third
energy energy energy
level level level
The first energy level is full when it has 2 electrons. All other energy levels are
full when they have 8 electrons.
Elements in the same group have the same number of electrons in their outer
energy level. It is only the outer electrons that are involved in chemical
reactions, this is why elements in the same group have similar chemical
properties.
All noble gases have full outer energy levels which makes them very stable.
The outer energy level is the
one furthest to the right.
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Ions
Ions are charged particles, i.e. contain a positive or negative sign.
Ions are atoms that have lost or gained electrons. We have to allow for this
when working out the number of electrons in a particular ion. To work out the
number of electrons in an ion use the following:
when a negative ion is shown add electrons
when a positive ion is shown take away electrons
the number of electrons to add or take away matches the size of the
positive or negative shown on the ion
Note: when an ion forms it is only the number of electrons that change,
everything else stays the same i.e. the number of protons and neutrons remain
the same.
Ion
Nuclide Notation Number of
Protons
Number of
Electrons
Number of
Neutrons
Cl-
3 1
Cl-
17
18
(17+1)
20
Mg2+
2412
Mg2+
12
10
(12-2)
12
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Electron Arrangement and Ions
Atoms always gain or lose the number of electrons required to achieve the same
electron arrangement as the nearest noble gas as noble gases are very stable
due to having full outer energy levels.
Metal atoms lose electrons to form positive ions.
For example,
Atom Ion
2412
Mg 2412
Mg2+
2,8,2 2,8 this is the electron
arrangement for the
nearest noble gas neon
number of protons = 12 number of protons = 12
number of neutrons = 12 number of neutrons = 12
number of electrons = 12 number of electrons = 10
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Non-metal atoms gain electrons to form negative ions.
For example,
Atom Ion
3 1
Cl 3 1
Cl-
2,8,7 2,8,8 this is the electron
arrangement for the
nearest noble gas argon
number of protons = 17 number of protons = 17
number of neutrons = 20 number of neutrons = 20
number of electrons = 17 number of electrons = 18
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Topic 2 Pupil Self Evaluation
Atomic Structure
Number
Learning Intention
Success Criteria
1 I will find out how to classify elements I can classify elements
2 I will find out about the rows and
groups of The Periodic Table
I can:
recognise a row or group in The Periodic Table
state the group name for groups 1, 7 and 0
identify a transition metal
describe chemical properties and trends in groups 1, 7 and 0
3 I will find out how to answer some
Problem Solving questions on Topic 2
I can answer some Problem Solving questions on Topic 2
4 I will find out about the structure of
the atom
I can:
state that all matter is made up of atoms
state that when a substance contains only one kind of atom it is
known as an element
state that an atom contains a nucleus
state the subatomic particles present in an atom
state the charge, mass and location in atom of these subatomic
particles
explain why atoms are neutral
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5 I will find out about the atomic number
of an atom
I can state:
the relationship between atomic number and number of protons
how atomic number effects the size and mass of atoms
how the elements are arranged in The Periodic Table according
to their atomic number
6 I will find out about the mass number
of an atom
I can:
state the relationship between mass number and number of
protons and number of neutrons
work out the mass number given the number of protons and
number of neutrons
7 I will find out how to work out the
atomic number, the number of protons,
the number of electrons, the mass
number and the number of neutrons of
an atom, given some information about
the atom
I can work out the following:
given the name of the element, work out the atomic number, the
number of protons and the number of electrons
given the name of an element and the number of neutrons it
contains, work out the mass number
given the name of an element and its mass number, work out the
number of neutrons
8E I will find out about nuclide notation I can:
represent an atom using nuclide notation
work out the number of protons, electrons and neutrons given
the nuclide notation of an atom
9E I will find out about isotopes I can state the definition of an isotope
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10E I will find out about Relative Atomic
Mass
I can:
state the definition of Relative Atomic Mass
given the RAM of an element, state which isotope is more
abundant and why
state why RAM’s are rarely whole numbers
11 I will find out about electron
arrangement
I can:
state how electrons are arranged in an atom
state the electron arrangement for a given element
state the number of electrons that make particular energy
levels full
explain why elements in the same group have similar chemical
properties
explain why The Noble Gases are stable
12E I will find out about ions
I can:
state the definition of an ion
work out the number of protons, neutrons, electrons and the
electron arrangement given the nuclide notation of an ion
explain why atoms lose or gain electrons
state whether metal and non-metals atoms gain or lose electrons
to form positive or negative ions
