Topic 3 – Atoms and the Periodic Table – Learning Outcomes
General Level
o Classify elements in different ways, eg naturally occurring/made by scientists; solid/liquid/gas;
metal/non-metal
o State that chemists have classified elements by arranging them in the Periodic Table
o State that a group is a column of elements in the Periodic Table
o State that elements in one group of the Periodic Table show similar chemical properties
o Identify the following families of elements: the halogens, the alkali metals, the noble gases, the
transition metals
o State that noble gases are a family of very unreactive elements
o State that every element is made up of very small particles called atoms
o Describe the atom as having a vary small positively charged nucleus with negatively charged
electrons moving around outside the nucleus
o State that an atom is neutral because the positive charge of the nucleus is equal to the sum of
the negative charges of the electrons
o State that atoms of different elements are different and have a different number on the Periodic
Table called the atomic number
o State the electron arrangements of the first 20 elements
o Explain the structure of the Periodic Table in terms of the atomic number and chemical
properties of the elements
o State that elements with the same number of outer electrons have similar chemical properties
o State that atoms of different elements vary in size and in mass
Credit Level
o Describe the location and charge of the proton, neutron and electron
o State the relative masses of the proton, neutron and electron
o State that an atom is neutral because the numbers of protons and electrons are equal
o State that atoms of different elements have a different number of protons, called the
atomic number
o State that the electrons in an atom are arranged in energy levels
o State that an atom has a mass number which equals the number of protons plus
neutrons
o Calculate the number of n, p and e from the mass number and atomic number, and vice
versa
o Calculate the number of n, p and e from nuclide notation (e.g. 4He), including ions
o State that most elements exist as a mixture of isotopes
o State what is meant by isotopes
o State what is meant by relative atomic mass
o Explain why the average atomic mass of an element is rarely a whole number.
Topic 3 Notes
Elements
The elements can be classified in many different ways:
 Naturally occurring and man-made
 Solid, liquid and gas
 Metal and non-metal
The elements are arranged in the periodic table
1
2
Transition Metals
34567
Groups in the periodic table go up and down and periods go across
the periodic table.
Chemists have given names to some of the groups in the periodic
table
 Group 1
Alkali Metals
 Group 2 Alkali Earth Metals
 Group 7 Halogens
 Group 8 Nobel Gases
 Between groups 2 and 3 we find the transition metals
Groups in the periodic table contain elements that all have similar
reactions
e.g. the alkali metals all react with water and the noble gases
are all unreactive
The Atom
All elements are made of small things called atoms. Atoms of
different elements are different, i.e. an oxygen atom is different
from a nitrogen atom.
Atoms are made of a nucleus with electrons orbiting around this
The nucleus itself is made up of protons and neutrons.
We can summarise what we know about each of these particles in
the following table:
Particle
Charge Mass
Protons
+
1amu
Neutrons
0
1amu
Electrons
0amu
(amu = atomic mass units)
Location
Nucleus
Nucleus
Orbiting Nucleus
We can see from this information that the protons are positive and
neutrons are neutral. This leaves the nucleus with an overall positive
charge. The electrons and negatively charged and orbit the nucleus.
In an atom the number of positive protons and negative electrons
are the same leaving the atom neutral.
All elements have an atomic number that is unique to them, oxygen is
8, and lithium is 7. This number is equal to the number of protons in
the nucleus of their atoms.
Since the protons and neutrons both have a mass of 1 and electrons
have no mass, the mass of an atom is only made from the
protons + neutrons.
Using the data book we can find out that lithium has a mass of 7.
We can also find out that lithium has 3 protons. This means that to
find the number of neutrons we just have to do; mass – no. protons
So 7-3 leaves us with 4 neutrons.
Element Protons Electrons Neutrons Mass
Lithium
3
3
4
7
8
16
23
Chemists have a special notation for elements showing the mass and
atomic number:
7
3Li
The mass number goes on top and the atomic number (number of
protons) goes on the bottom before we write the symbol for that
element.
Electron Arrangement
The electrons in atoms do not just move around randomly. They are
arranged in energy levels. The first energy level can hold 2
electrons and the rest can hold up to 8.
These diagrams help to explain page 1 of the data book. Page 1 tells
us the electron arrangement for all the elements. We are just
interested in the first 20 in standard grade and we can use this
information on page 1 to draw target diagrams for the first 20
elements.
Elements in the same group have the same number of outer
electrons
e.g. lithium, sodium, potassium etc all have one outer electron. This
explains why elements in the same group have similar chemical
reactions.
Isotopes
Atoms of the same element can have different masses. Chlorine has
two types of atoms, one with a mass of 35 and another with a mass
of 37. Both atoms have 17 protons as this is what makes the atom
chlorine. The difference is the number of neutrons.
Atoms of the same element with different masses are called
isotopes. This leads to scientists working out the average mass of
elements (the relative atomic mass). Chlorine has a relative atomic
mass of 35.5. This is the average of the two isotopes (mass 35 and
37). The reason the average is not 36 is because there is more of
the 35 isotope than the 37.
Practise Questions
07 General: 1b, 6b, 8a
07 Credit: 7, 10a, 10b
08 General: 1a, 2b
08 Credit: 15
09 General: 1, 8, 10a
09 Credit: 7, 9,