Fundamental Particles

What are atoms made out of

subatomic particles- protons, neutrons, electrons

Structure of atom

• protons and neutrons form the nucleus in centre of atom

• protons and neutrons called nucleons b/c found in nucleus - nucleons contain all the mass in the atom

• electrons surround and are found in series of levels in shells/orbits at different distances form nucelus

Relative mass of proton , neutron and electron

proton: 1

neutron: 1

electron: 1/2000

relative charge of protons , neutrons and electrons

proton: +1

neutron: 0

electron: -1

Why atom neutral

number of electrons same as number of protons b/c charge is equal in size and opposite in sign so cancel out e/o to make atom neutral in charge

Arrangement of subatomic particles

• protons + neutrons in centre of atom held together by force called strong nuclear force

• much stronger than electrostatic force of attraction that holds electrons and protons together in atoms

• hence strong nuclear force overcomes repulsion between the protons in the nucleus

• nuclear force only acts over small distances within nucleus

Atomic number(z)

number of protons in nucleus of atom ( bottom number)

What determines the chemical identity of an element

atomic number

What determines the chemical proeprties of an element

• number of electrons in outer shell of atom determiens the chemical prorpties of the atom (how it reacts)

mass number(A)

total number of protons and neutrons in nucleus of an atom( top number)

what is an isotope

• atoms of the same element with the same number of protons (and hence same number of electrons) but different number of neutrons in their nuclei

• vary in mass number b/c of different number neutrons called isotopes

How do isotopes react chemically and why

• different isotopes of the same element react chemically in the same way b/c they have the same electron configuration- isolectronic( same number of electrons)

• reactivity depedns on number and arrangement of electrons

What is the most common GCSE example of isotopes

• 35Cl and 37Cl : stable and both naturally occur

• all elements have isotopes but usually one is much more stable

What is mass number - atomic number

number of neutrons

Physical Properties

• isotopes have different masses so may appear more dense than the other

• different mass of an isotopes affects how much energy is required

• heavier molecule move more slowly, have lower vibrational energy- requires more energy to melt/boil etc(kinetic isotope effect)

Definition of RAM (relative atomic mass)

• RAM of an element: weighted average (relative abundance ) of masses of atoms of isotopes compared to 1/12th mass of one carbon -12 atom.