Chemistry GCSE: Atoms + Elements + Compounds + Mixtures

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==