Science- chemistry notes

Definitions:
Atoms: Tiny particles that make up all matter. Atoms are made up of protons, neutrons and electrons. Protons and neutrons are heavier than electrons and are located at the centre of the atom, the nucleus. The electrons spin around the nucleus in a region of empty space.

Neutrons are neutral-no charge.

Protons-have a positive charge.

Electrons-have a negative charge.

Opposite charges attract each other and this is what keeps the electrons from spinning out of the atom.

Atoms are neutral-same number of electrons and protons

Number of Protons-atomic number

Number of protons and neutrons-mass number

First shell Second shell Third shell Fourth shell
Maximum of 2 e- Maximum of 8 e- Maximum of 18 e- but stable with 8 e- Maximum of 32 e- but stable with 8 e-

Electron shell rules

Elements: pure substances made of only one type of atom.

Compounds: Pure substances made up of two or more different types of atoms. The atoms are chemically bonded to each other.

For example: 2 hydrogen atoms and 1-oxygen atoms are bonded together to form h20.

A substance is only pure if it isn’t mixed with anything. Compounds and elements are pure mixtures aren’t.

Molecule: A group of atoms bonded together. Make up compounds.

Lattice: Much larger bonded structures.

Mixtures: Different elements and compounds thrown together.
Periodic table of elements
Periodic Table of Elements

Newlands- arranged 60 or so known elements in columns of increasing atomic mass.

Meedeleev- arranged the known elements into horizontal rows of increasing atomic mass and put the known families into vertical columns. Left room for undiscovered elements.

Meyer- created table at same time as Meedeleev by comparing the physical properties of elements with atomic mass. He though did not leave room for undiscovered elements. Although he is known as a joint ‘father’ of the periodic table.

Moseley- he suggested that the physical and chemical properties were relate to the atomic number, rather than mass. He improved the previous tables to come up with a more accurate one with fewer errors and fewer missing elements.

Features of the table

*About 80% of elements-metals

*The left hand side- metallic

*Bottom left- most reactive

*Right hand side-generally non-metal

*Upper right-most reactive non-metals

*Group 8-chemically inert

*Separating metals and non-metals- metalloids

*3 special blocks-transition elements, lanthanides and actinides. All metals, many of lanthanides and actinides are radio active.

Metals and Non-Metals

Metal-properties
*Conductors of heat and electricity
*Lustrous-shiny
*Malleable-can be hammer into new shapes
*Solid at room temp-except mercury-liquid
*High densities
*Atoms that form lattices
*Ductile-can be stretched into wires

Non-Metal-properties
*Poor conductors or insulators-except carbon
*Low melting and boiling points
*Brittle
*Dull-not shiny
*Group 8 cant exist as single atoms
*Most form molecules few form lattices

Reactivity

Group VIII contains elements that are stable are rarely react. All other atoms though react so that they can become as stable as the noble gases. They also want a full outer shell or 8 electrons. To do this atom gain electrons loose electrons and sometimes share electrons.

Chemical change

New substances are formed in a chemical change. Can’t be undone.
E.g.:
*Food is cooked
*Fruit and vegetable ripen
*Something is burnt something explodes

E.g.
*Fireworks explode
*A banana ripens

Occurs everyday

Signs of a chemical change:
*Permanent colour change
*A gas is given off
*A precipitate forms
*Energy is produced or absorbed

Ions

If the number of electrons changes in an atom, it becomes electrically charged and is called an ion.
*If an atom looses electrons it becomes a positive