Matter & The Atom

Matter The term matter describes all of the physical substances around us Matter is anything that has mass and takes up space The Universe is made up of matter and energy

Matter is made up of atoms. An atom is the smallest whole particle of matter. Subatomic particles are smaller than atoms and are the tiny particles that an atom is made of.

Early Models of the Atom Rutherford Mostly empty space Small, positive nucleus Contained protons Negative electrons scattered around the outside

Early Models of the Atom Bohr Electrons move in definite orbits around the nucleus

Modern Model of the Atom The Electron Cloud Sometimes called the wave model Spherical cloud of varying density Varying density shows where an electron is more or less likely to be

Atomic Structure Nucleus –Protons –Neutrons Electrons

Atomic Structure Electrons Tiny, very light particles Have a negative electrical charge (-) Move around the outside of the nucleus

Atomic Structure Protons Much larger and heavier than electrons Protons have a positive charge (+) Located in the nucleus of the atom

Atomic Structure Neutrons Large and heavy like protons Neutrons have no electrical charge Located in the nucleus of the atom

Atomic Structure

Describing Atoms Atomic Number (Z) = number of protons In a neutral atom, the # of protons = the # of electrons Mass Number (A) = the number of protons + the number of neutrons

Ions An atom that carries an electrical charge is called an ion. If the atom loses electrons, the atom becomes positively charged (because the number of positively charged protons will be more the number of electrons).

Ions If the atom gains electrons, the atom becomes negatively charged (because there are more negative charges than positive).

Ions The number of protons does not change in an ion. The number of neutrons does not change in an ion. So, both the atomic number and the atomic mass remain the same.

Ions One more proton means one more positive charge. This makes the total charge of the atom POSITIVE. This atom has lost an electron. Now it has one more proton than electron.

Ions This atom has gained an electron. Now it has one less proton than electron. One less proton means one less positive charge. This makes the total charge of the atom NEGATIVE.

Isotopes The number of protons for a given atom never changes. The number of neutrons can change. Two atoms with different numbers of neutrons are called isotopes Isotopes have the same atomic # Isotopes have different mass # ’ s

Isotopes

Average Atomic Mass The average atomic mass is the weighted average mass of all the naturally occurring isotopes of that element.

Average Atomic Mass You are NOT responsible for knowing how to calculate average atomic mass. The average atomic mass of the element is the sum of the mass contributions of each isotope.