Chemistry

Law of Conservation of mass

In a chemical reaction, matter s neither created nor destroyed.

Mass of reactants= mass of products

Antoine Lavoisier

Law of definite proportions

All samples of a given compound have the same proportions of their constituent elements

Joseph Proust

Law of multiple proportion

When 2 elements form 2 different compounds, the masses of one element can combine with 1g of another element, and this can be expressed as a ratio of small whole numbers

Matter

anything that occupies space and has mass

Physical property

a property that a substance displays without changing its composition

Chemical property

a property that a substance displays only by changing its composition

cation

positive charged ions

anion

negative charged ions

Mole concept

the bridge between the number of particles in a substance and its mass

interference

the interaction between waves

emission spectra

Closer inspection of the light emitted by various atoms reveals that it contains several distinct wavelengths.

The emission spectrum of a particular element is always the same— it consists of the same bright lines at the same characteristic wavelengths—-- and we can use it to identify the element

Coulombs Law

describes the attractions and repulsions between charged particles

For like charges, the potential energy is positive and decreases as the particles get further apart as r increases

For opposite charges the potential energy is negative and becomes more negative as the particles get closer together

Shielding

In a multi electron atom, each electron experiences both an attraction to the nucleus and the repulsion from other electrons in the atom. These repulsions cause an electron to experience a net reduction in attraction to the nucleus

Noble gases

Do not react

have 8 valence electrons (except He which has 2)

Atomic radii

atomic radius increases down a group and decreases across a period