2.1 Nature of Matter

Atoms• Atoms are the basic unit of matter

• Theorized by Democritus, 2500 yrs ago

• Composed of 3 subatomic particles– Protons– Neutrons– Electrons

Nucleus

• Center of the atom

• Made up of the protons and neutrons– Protons (+) charge– Neutrons (= or neutral) charge

• # of protons and neutrons make up the atomic mass number

Electrons• Very important in bonding with other elements• (-) charge• Attracted to the positively charged nucleus• Remains outside the nucleus in a cloud• Usually has the same number of electrons as

protons• Maintains electrically neutral atoms• Very small compared to protons and neutrons

Elements

• A pure substance that consists of entirely of one type of atom

• A list of all the elements can be found in the periodic table

Isotopes

• Elements which have different numbers of neutrons

• All isotopes have the same number of protons giving them the same properties

Isotopes• Can be radioactive- unstable nuclei that

breakdown over time

• Can be used for many things-– Dating materials– Detect and treat cancers– Kill bacteria

Chemical Compounds

• Substance formed by the chemical combination of two or more elements

• Always form in the same proportions– EX: H2O, CO2

• Chemical compounds have very different characteristics compared to their elemental components.

NaCl

• Sodium- silvery, white metal– Explosive, if exposed to oxygen

• Chlorine- poisonous green gas– Extremely harmful to humans

+ =

Chemical Bonds• Ionic and covalent bonds are the main types

of bonds • Ionic- forms between metals and nonmetals

– Forms through a transfer of electrons• Covalent- forms between two nonmetals

– Produced through a sharing of electrons