Revising Unit 1 Chemistry Atomic Structure
Learning Objectives
Answer
1.1: Describe how the Dalton model of the
atom has changed over time because of the
discovery of subatomic particles
● Dalton thought that atoms were _________
● described atoms as______ ________,
● modern ideas about atoms suggest atoms are made up of
________ particles such as protons _______ and
_________.
Protons
solid spheres
smaller indestructible neutrons
1.2 Draw the structure of the atom as
nucleus containing protons and
neutrons, surrounded by electrons in
shells.
1.3 Recall the relative charge and
relative mass of
a: a proton, b: a neutron & c: an electron
Particle
Mass
ChargeRelative mass Relative
crge
Proton
Neutron
Electron
1.4 Explain why atoms contain equal
numbers of protons and electrons.
Atoms are _______ - they have no charge overall
The charge on electrons is the same size as the charge on
the ______- these charges cancel out.
This is why atoms contain the ______ number of protons as
electrons.
Same
1.5 Describe the nucleus of an atom
as very small compared to the overall
size of the atom
1.6 Recall that most of the mass of
an atom is concentrated in the
nucleus.
protons
neutral
The nucleus:

is in the _________of the atom.

It contains _______ and _______.

It has a _______ charge because of the _______.

It has almost the whole _______ (of the atom)
concentrated in the nucleus (1.6)

It is _______ compared to the overall size of the atom
Tiny mass protons positive neutrons centre
1.7 Recall the meaning of the term mass
number of an atom

1.8 Describe atoms of a given element
as having the same number of protons in
the nucleus and that this number is
unique to that element
The atomic number tells you how many protons/neutrons
an atom has.

Every atom of an element has the same number of
protons/neutrons.
1.9 Describe isotopes as different atoms
of the same element containing the
same number of protons but different
numbers of neutrons in their nuclei
Isotopes are different forms of the same element which have:

the same atomic number (number of neutrons
/protons)

different mass numbers (different numbers of protons
/neutrons)
1.10 Calculate the numbers of protons,
neutrons and electrons in atoms given
the atomic number and mass number
Number of protons (same as atomic number) =___
In any atom: No. of protons =No. of electrons
Hence, no. of electrons = ____
No. of neutrons = mass no. – atomic no. =
1.11 Explain how the existence of
isotopes results in relative atomic
masses of some elements not being
whole numbers


1.12 Calculate the relative atomic
mass of an element from the
relative masses and abundances
of its isotopes [Higher only]
If an element has more than one isotope, its mass no. is
the average of the mass numbers of all the different
isotopes, taking into account how much there is of each
one. So, it might not be a whole number.
Eg., chlorine has two stable isotopes, chlorine-35 and
chlorine-37. There’s quite a lot of chlorine-35 around and
not so much chlorine-37 — so chlorine’s mass no. works
out as 35.5.
Chlorine naturally exists as two isotopes,
and
(chlorine-35)
(chlorine-37).
The abundance of chlorine-35 is 75% and the abundance of
chlorine-37 is 25%.
To calculate the relative atomic mass, Ar, of chlorine:
(to 1 decimal place)
Note. The answer is closer to 35 than it is to 37. This is
because the chlorine-35 isotope is much more abundant than
the chlorine-37 isotope.
1.13 Describe how Mendeleev arranged
the elements, known at that time, in a
periodic table by using properties of
these elements and their compounds

Sorted elements (and their compounds) with similar
________ properties into groups,

In order of atomic______,

this showed a _________
mass chemical pattern
1.14 Describe how Mendeleev used his
table to predict the existence and
properties of some elements not then
discovered
1.15 Explain that Mendeleev thought he
had arranged elements in order of
increasing relative atomic mass but this
was not always true because of the
relative abundance of isotopes of some
pairs of elements in the periodic table

Mendeleev ______ the chemical and physical properties
of an element he called_______, which we know today as
germanium.
Ekasilicon predicted

Mendeleev ordered elements by decreasing /increasing
atomic mass but he was wrong (due to the presence
of_________ ) which he did not know about
 some elements just didn’t quite fit the pattern
 he ________ the order of the elements to keep those with
the ______ properties in the same columns
switched isotopes same
Eg., Iodine has a lower relative atomic mass than tellurium.
So iodine should be placed before tellurium in Mendeleev's
table. However, iodine has similar chemical properties to
chlorine and bromine. To make iodine line up with chlorine
and bromine in his table, Mendeleev swapped the positions of
iodine and tellurium. iodine and tellurium were reversed in
Mendeleev's table because:
 iodine has one naturally occurring isotope, iodine-127
 the most abundant tellurium isotopes are tellurium-128 and
tellurium-130
 The high relative abundance of these tellurium isotopes
gives tellurium the greater relative atomic mass.
 The atomic number of tellurium is 52 and the atomic
number of iodine is 53, so these elements are in the correct
order in the modern periodic table.

1.16 Explain the meaning of atomic
number of an element in terms of
position in the periodic table and number
of protons in the nucleus

atomic number of an atom is the number of _______ it
contains

All the atoms of a particular element have the _____
atomic number (number of protons)

atoms of different elements have _____ numbers of
protons.
Different
protons
same
1.17 Describe that in the periodic table
a. elements are arranged in order of
increasing atomic number, in rows called
periods
b. elements with similar properties are
placed in the same vertical columns
called groups
In the periodic table the elements are arranged into:
a. Rows, called _____, are organised in order of
increasing atomic _____
- the period to which the element belongs corresponds
to the number of _____ of electrons it has.
b. Vertical columns, called _______, where the elements
have _______ properties
Shells
1.18 Identify elements as metals or nonmetals according to their position in the
periodic table, explaining this division in
terms of the atomic structures of the
elements

similar
periods
number
group
In the modern periodic table, the elements are arranged
according to their atomic number - not their relative atomic
_____.

The metal elements are found on the _____ hand side of
the periodic table, and the non-metal elements are found
on the _____.
Right
1.19 Predict the electronic configurations
of the first 20 elements in the periodic
table as diagrams and in th e form, for
examp le 2.8.1
mass
left
Predicting an electronic configuration
The electronic configuration of an atom can be predicted from
its atomic number.
For example, the atomic number of sodium is 11. Sodium
atoms have 11 protons and so 11 electrons:
The electronic configuration of sodium (2.8.1) shows that
sodium, Na:

is in period __

is in group __

has an atomic number of ___
1
1.20 Explain how the electronic
configuration of an element is
related to its position in the periodic table
3
11
An electronic configuration is the way in which electrons are _____
in an atom.
Electrons in shells

Different shells can hold ________ numbers of electrons.

Electrons occupy shells starting with the __________one.

They begin to occupy the next shell when a shell
becomes______.
Full
innermost
different
arranged