1. Science Ascending means least to greatest or small to big
8/18/2017
BBC - GCSE Bitesize - Atomic structure
Science
Atomic Structure part 1
All substances are made from atoms. Each atom is made of a nucleus - containing protons and neutrons - surrounded by electrons.
The atomic number is the number of protons in an atom. The elements are arranged in the periodic table in ascending order of atomic number.
The mass number of an atom is the total of protons plus neutrons..
Atomic Structure part 2
All things are made from atoms. There are just over one hundred different types of atom, called elements. Atoms can join together in millions of different combinations to make all the substances on Earth and beyond.
Every atom is made of a nucleus consisting of protons and neutrons. The nucleus is surrounded by electrons. Protons and electrons are oppositely charged. Neutrons have no charge. This means the nucleus of an atom is always positively charged.
Ascending means least to greatest or small to big
Substances = things
Structure of the atom
An atom has a neutral overall charge because it has the same
number of electrons as protons.
Protons and neutrons have the same mass. Electrons have such a small mass that this can usually be taken as zero.

2. Arranged means organized
The atomic number is the number of protons in an atom.
The mass number is the total number of protons and neutrons in an atom.
The elements are arranged in the periodic table in ascending order of atomic number so it's easy to find the name or symbol for an atom if you know the atomic number.
Arranged means organized
The chemical symbol for carbon
Atomic Number
Chemical Symbol
Mass Number
An atom of carbon has six protons (because its proton number, at the top, is 6) and Six electrons (because the number of protons and electrons in an atom is the same)
The mass number at the bottom tells us that the total number of protons and neutrons in a carbon atom is 12.
You can find out the amount of neutrons by using the formula Mass number- Atomic number=Neutrons

3. 8/18/2017
BBC - GCSE Bitesize - Atomic structure
Energy shells
Electrons are arranged in different shells around the nucleus The innermost shell -or lowest energy shell - is filled first. Each succeeding shell can only hold a certain number of electrons before it becomes full. The innermost shell can hold a maximum of two electrons, the second shell a maximum of eight, and so on. The table gives the maximum capacity of the first three shells.
Maximum capacity of the first three shells
Maximum number of Electrons
Innermost shell or lowest energy shell means the shell closest to the nucleus.
First Shell Second Shell Third Shell
2 electrons
8 electrons
A lithium atom, for example, has three electrons. Two are in the first energy shell, and one in the second.
A carbon atom has six electrons. Two are in the first energy shell, and four in the second energy shell.
Lithium
Carbon