Atoms

The Nucleus

• It’s in the middle of the atom

• It contains protons and neutrons

• The nucleus has a radius of around 10x-14

• It has a positive charge because of protons

• Almost the whole mass if the atom is concentrated in the nucleus

The Electrons

• Move around the nucleus in the electron shells

• They’re negatively charged and tiny, but they cover a lot of space

• The volume of their orbits determines the size of the atom

Electrons have virtually no mass

Protons, Electrons, Mass Number, Atomic Number

• Atoms are neutral

• They have the same number of protons as electrons

• The charge on the electrons is the same size as the proton but opposite

• In an ion the number of protons doesn’t equal number of electrons

• The nucleus symbol of an atom tells you its atomic number and mass number

• The atomic number tells you how many protons there are

• The mass number tells you the total number of protons and atoms

• To get the number of neutrons just atomic number - mass number

Elements

Elements consist of Atoms

• Atoms can have different numbers of protons and electrons

• If a substance only contains contains atoms with the same number of protons its an element

• All atoms of an element have the same number of protons

• Elements are represented by a one or two letter symbols

Isotopes

• Isotopes are different forms of the same elements, they have the same number of protons but different numbers of neutrons

• They have different mass and atomic numbers

• Elements can exist as a number of different isotopes

• Relative atomic mass is used to refer to the element as a whole, this is the average mass of the element

Relative atomic mass= (isotope abundance x isotope mass number)/ sum of abundance of all isotopes

Compounds

• Atoms combine with other atoms of different elements to form compounds

• These atoms are of fixed proportion and held together by chemical bonds

• Making bonds involves atoms giving, taking or sharing electrons

• Metal + Non-Metal elements consists of ions, the metal atoms lose electrons to become positively charged, the non-metal atoms gain electrons to become negatively charged

• A compound formed from non-metals consists of molecules, each atoms shares an electron with another atom - this is covalent bonding

• The properties of a compound are usually totally different from the properties of the original elements

Mixtures

• There’s no chemical bond between different parts of a mixture

• The parts of a mixture can be separated out by physical methods

• Air is a mixture of gases, they can all be separated out fairly easily

• The properties of a mixture are just a mixture of the properties of the separate parts