Molecules and atoms

What is an atom?
An atom is the smallest particle of an element. It cannot be split into anything smaller by a chemical reaction.[image]
What is an element?
There are only just over a hundred different elements in the Universe. They are listed in the periodic table. An element only contains one type of atom.[image]
What does the periodic table do?
It lists all of the elements in the order of their atomic number . They are arranged in columns called groups and rows called periods. The groups are like families of elements that resemble each other in the way they behave.[image]
What is a Group of elements?
A column in the periodic table of elements that belong to the same ‘family’ – they all have similar behaviours.
What is a period of elements?
A row of the periodic table. All of the elements have different properties as you move across the table.
What is the name of group 0?
The Noble gases or inert gases as they don’t usually react with anything!


What is the name of group VII (7)?
The halogens which means the salt givers. They are very reactive – the most reactive one is at the top of the group!


What is the name of group I (1)?
The alkali metals. They are very reactive…. and get more reactive as you go down the group.


What is an atom made of?
An atom has a tiny nucleus and is orbited by electrons (like the Sun orbited by planets).


What is inside the nucleus of an atom?
Protons (yellow in the diagram!) – the number of these tells you which element the atom is part of. They have a positive charge…. and neutrons (shown in orange) – we will come to them later!…. they have no charge.


What is important about the number of protons in the nucleus?
The number of protons in the nucleus is called the proton number by physicists but chemists call it the atomic number. The number of protons determines the number of electrons orbiting the atom. There are always the same number of electrons as protons in a neutral atom… and it is the arrangement of the electrons that governs how the atom reacts with other atoms. They react to get a full outer shell.
What is the atomic number?
The proton number of the atom – the number of protons in the nucleus.
What is a molecule of an element?
A molecule of an element is made when two or more atoms of that element join together. For example gaseous oxygen atoms go round in pairs, so do nitrogen, fluorine and chlorine atoms. They do this if they are very reactive. They share their electrons to obtain a full shell configuration


What is a compound?
A compound is made up molecules that contain two or more different types of atom bonded together.


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