What do you remember from Year 10? What is the periodic table? What is the atomic number? What is the atomic mass? How many protons are in neon? What is the difference between elements and molecules? On which side of the periodic table do metals occur?

What does each box in the periodic table represent?

Elements (notes) The periodic table is a table of all known elements, currently there are 117 known elements The tremendous variety of matter in our world is due to combinations of only about 100 very basic or elementary substances called elements. An element is composed of a unique kind of atom and when lots of the same type of atoms are together you have a pure chemical substance. Atoms are the building blocks of matter Atoms contain particles called Protons, Neutrons and electrons Molecules are made up of two or more types of atoms

The Beginning of Chemistry Developing the periodic table

Ancient Chemistry Humans have been playing with chemicals for thousands of years; cooking food, making clay pots and making iron. Empedocles (450 BC) Proposed that all matter was made from four substances – earth, air, fire and water. Democritus (450 BC) Suggested that everything was composed of minute, invisible, indestructible particles of pure matter.

Alchemists (16th and 17th Century) Alchemists were occupied with trying to change metals into gold and finding the elixir of life (magic in other words) It was believed that an essential ingredient to these was the philosophers stone (of the Harry Potter fame) Discoveries were made by trial and error. Discovered elements: S, Hg, C, Fe, Pb, Cu, Sn, Ag, Au, P, As, Sb, Bi, Zn.

Robert Boyle (1661) Chemistry started becoming a science It all started with the finding elements Boyle defined what an element was, an “unmingled bodies” Suggested the concept of an element as a pure substance and of compounds being formed from a combination of elements. Also developed Boyle's Gas laws

Priestley (1774) Did important research on gases He collected the gas when mercury oxide decomposed by heating What do you think the gas was? Oxygen So he was the first person to isolate elemental oxygen

Phlogiston Theory In addition to water, earth, wind and fire scientists in the late 1600s believed there was another fire-like element called "phlogiston" that was contained within combustible bodies, and released during combustion But Lavoisier found when magnesium is burned in a crucible it gains weight This could not be explained by phlogiston theory

Lavoisier (1785) Contributed to the law of conservation of mass Abolished the phlogiston theory What is the law of conservation of mass? During a chemical reaction, the mass of reactants is equal to mass of the products

Dalton (1805) John Dalton's famous theory was on the conservation of matter. He based this theory on these five statements. All matter is composed of very small particles called atoms. Atoms in the same element have the same properties Atoms can neither be destroyed, created, or divided. When atoms of different elements are combined, they form chemical compounds. A chemical reaction will occur when atoms are combined, rearranged or separated.

Berzelius (1828) Prepared, purified and identified many chemical elements and hundreds of compounds. Proposed the idea of using letters as symbols. Calculated relative atomic masses of elements.

Mendeleev (1869) Constructed the periodic table Period Law – chemical properties varied periodically with increasing atomic weights. Arranged elements with similar chemical properties in vertical groups. Arranged the elements in order of increasing relative atomic mass into horizontal periods. Left gaps in the table for as yet undiscovered elements.

Elements, Compounds and Mixtures Element – a substance composed of atoms with the same atomic number. Compound – formed when 2 or more different elements join together chemically in set proportions to form a new substance. Mixture – formed when different proportions of elements are combined together (not a chemical bond). Molecule – 2 or more non-metal atoms chemically combined.

The difference between compounds and molecules A molecule deals with at least 2 atoms e.g. Oxygen (O2, H2) A compound deals with 2 different elements (H2O Some elements naturally appear together like oxygen, O2. When there are two atoms together, it is called a molecule.