All substances are made of Atoms.
An Atom is the smallest part of a substance.
An element is a substance made of only one type of atom.
They are found on the periodic table.
There are about 100 elements.
Around 80 are metals and around 20 are non-metals.
Each element has a symbol which is either:
A capital letter e.g Hydrogen is H
Or a capital followed by a small letter e.g. Zinc is Zn
In the early 1800s John Dalton suggested that atoms were like tiny snooker balls and that all substances were made up of different cominations of a few different types of atom.
In 1897, JJ Thomson discovered the electron and suggested that they were like tiny plum pudding balls of positive charge with negative electrons stuck inside.
1911, Ernest Rutherford suggested that atoms had a central nucleus containing smaller particles called protons which were positive.
Niehls Bohr and James Chadwich
1913, Niehls Bohr said electrons orbited the central nucleus. In 1932, James Chadwich discovered neutrons.
So as more experiements were done and more evidence was gathered, ideas about the structure of atoms were updated. We currently use the nuclear model.
Protons: Neutrons: Electrons:
Charge: 1+ Charge: 0 Charge: 1-
Atomic Mass: 1 Atomic Mass: 1 Atomic Mass: 0(almost)
Isotopes are atoms of the same element that have a different number of neutrons.
A mixture consists of 2 or more substances which have not chemically reacted together. e.g. white coffee, salt solution.
The chemical properties of the components in the mixture don't change.
The components can be separated again by:- evaporation, condensation, distillation, filtration and chromatrography.