atomic structure KS4

atom

the smallest part of an element

element

a substance only made up of one atom

compound

a substance made up of two or more atoms chemically bonded eg H20

mixture

a substance made up of two or more atoms/compounds not chemically bonded eg air

protons

a mass of one, plus one charge, and found in the nucleus

electrons

a mass of 1/2000/negligible, minus one charge, found on the electron shells

neutrons

mass of one, neutral charge, and found in the nucleus

plum pudding model

• randomly scattered electrons

• sphere of positive charge

nuclear model

• mostly empty space

• electrons on orbitals

• dense, positive nucleus

discovery of the atom - early 1800’s

dalton stated that the atom is an indivisible sphere

discovery of the atom - 1897

discovery of the electron by JJ Thomson

discovery of the atom - late 1800’s

Thomson proposed the plum pudding model

discovery of the atom - 1909

discovery of the nucleus

discovery of the atom - 1913

discovery of the electron shells by Niels Bohr

discovery of the atom - after Bohr’s discovery

Rutherford proposed the nuclear model

discovery of the atom - 1917

discovery of protons by Ernest Rutherford

discovery of the atom - 1932

discovery of the neutrons by James Chadwick

alpha particle scattering/gold foil experiment (RUTHERFORD)

using the plum pudding model, they thought that most alpha particles would pass through the atom, but more particles than expected deflected which suggested that there was something in the nucleus stopping it (protons and neutrons)

mass number

number of protons + number of neutrons

atomic number

number of protons (equal to electrons)

isotope

atoms of the same element with the same number of protons (and same number electrons) but have a different number of neutrons

why do isotopes have identical chemical properties

isotopes have the same number of electrons so react similarly

why do isotopes have different physical properties

isotopes have a different number of neutrons, so the mass number is different

name four physical properties that are different in isotopes

mass, density, melting point, and boiling point

relative atomic mass

the average mass of all isotopes of an element, compared to carbon-12

relative atomic mass formula

sum of (isotope mass X abundance) / total abundance

chemical property

how the substance reacts

physical property

what the substance looks like, mass, density

group number

tells you how many electrons are on the outer shell

period number

tells you the number of electron shells

ion

an atom that has lost or gained electrons

metals forming ions details + charges

lose electrons, form positive ions, group 1- plus one, group 2 - plus two, group 3 - plus three

non metals forming ions details + charges

gain electrons, form negative ions, group 7 - -1, group 6 - -2, group 5 - -3