The document discusses the structure of atoms. It explains that atoms are made up of a nucleus containing protons and neutrons, surrounded by electrons. The number of protons determines the element, while the number of neutrons determines the isotope. Electrons determine chemical properties and are equal to the number of protons. The periodic table arranges elements in order of atomic number and can be used to look up each element's protons, neutrons, and electrons. Isotopes are variants of the same element with different numbers of neutrons. Compounds contain two or more elements chemically bonded together, and their formulas show the number of atoms of each element. The electronic structure shows how electrons fill different energy levels around the nucleus.

1. C3a What are Atoms Like?
What is an atom?
What is the structure of an atom?
• Atoms are made up from a central ___________ that is orbited by __________
• The nucleus is made up of ________________ and ____________________.
• So, atoms are made up from 3 sub-atomic particles; ______________,
_______________ and _____________________.
What are protons, neutrons and electrons?
sub-atomic particle charge mass
protons
neutrons
electrons
IMPORTANT FACT
An atom always has an ____________ number of ________________ (+) and
________________ (-). This means that they have no overall charge – we say
that they are ______________________.
How can we work out the number of protons, neutrons and electrons in an atom?

2. • Each different type of atom is a different ______________ and has a
different number of ____________, ____________ and ______________.
• Everything on Earth is made up from about _________ different elements and
they are listed on the periodic table:
23
Consider Sodium
Each element can be found in its own square. Find sodium and copy the information
into this box:
What can we tell from this information?
Na
sodium
Tasks

3. 1. Using a periodic table, find the symbol and the atomic number for:
a) Helium
b) Potassium
c) Iron
d) Copper
e) Bromine
2. Complete the following table:
Name Symbol Atomic Number Mass Number
Lithium Li 3 7
Carbon
Calcium
Aluminium
Iron
3. Now calculate the number of protons, neutrons and electrons in one atom of
each element from the table above.
Remember: Atomic number = number of protons (there must be an equal number of electrons)
Mass number = number of protons + neutrons
Name Number of protons Number of neutrons Number of Electrons
Lithium 3 7-3 = 4 3
Carbon
Calcium
Aluminium
Iron
How are elements arranged in the Periodic Table?
Find the following elements, in order, Hydrogen
Helium
Lithium

4. Beryllium
Boron
Carbon
Nitrogen
Oxygen
Fluorine
Neon
Sodium
What do you notice about the atomic numbers and atomic masses of these elements?
Give as much detail about any trends (patterns) that you spot. Answer in bullet points.

5. Scientists use isotopes to carbon-date dinosaur bones and other fossils.
Isotopes
• Isotopes are different varieties of the same element.
• Isotopes have:
the same __________________ but different _______________
or the same number of ___________ but different numbers of _______
• Carbon is an element that has 2 isotopes called carbon-12 and carbon-14
Carbon-12 Carbon-14
12 14
6 C 6 C
Number of:
protons =
neutrons =
electrons =
Important:
The neutrons do not affect the __________________________ of an element so
different _____________________ of an element perform EXACTLY THE SAME
chemical reactions they are just heavier.
Task
Hydrogen has 3 isotopes. They have mass numbers of 1, 2 and 3. Calculate the number
of protons, neutrons and electrons for all 3 different isotopes of hydrogen.

6. Compounds
• An element is a substance which:
1.
2.
• A compound is a substance that contains at _____ or more _________ chemically
bonded together.
• You must be able to identify the elements in a compound from its formula, using a
periodic table
e.g. CuSO4 contains: _____ atom of the element copper, Cu
_____ atom of the element sulphur, S
_____ atoms of the element oxygen, O
Task
Identify which elements make up the following compounds and how many atoms of
each element there are. The first one is done as an example (it continues on the next
page.
a) MgO f) C6H12O6
Mg Magnesium – 1 atom
O Oxygen – 1 atom
b) K2O g) Al2O3
c) CO2 h) Fe(OH)2

7. d) NaOH i) KCr2O7.6H2O
e) P2O5 j) CuSO4.5H2O
Electronic Structure
• The electronic structure shows us how electrons are arranged in an atom.
• Electrons occupy the space around the _______________.
• Electrons ___________ the nucleus in _____________ (sometimes called
energy levels).
• Electrons must fill the ________ shell, which is closest to the nucleus before
they can start to fill the _______ shell.
• The 1st shell can hold a maximum of _____ electrons
The 2nd shell can hold a maximum of _____ electrons
The 3rd shell holds a maximum of _____ electrons before starting the 4th shell.
e.g. sodium has 11 electrons so the electronic arrangement for sodium is:
Calcium has 20 electrons so the electronic arrangement for calcium is:
For your exam:

8. You must be able to deduce the electronic structure of the first 20
elements in the periodic table e.g. calcium is 2.8.8.2.
Element Atomic Electronic Structure Group
Number Number
H 1 no number
He 2
Li 3
Be 4
B 5
C 6
N 7
O 8
F 9
Ne 10
Na 11
Mg 12
Al 13
Si 14
P 15
S 16
Cl 17
Ar 18
K 19
Ca 20
What do pattern do you notice in the number of electrons in the outer shell and the
group number of each element?