atomic structure KS4

atom: the smallest part of an element

element: a substance only made of one type of atom

compound: a substance made up of two or more atoms chemically bonded eg H2O

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


PROTONS, ELECTRONS, AND NEUTRONS

Protons have a mass of 1, a +1 charge/positive, and are found in the nucleus. Electrons have a mass of 1/2000 (can also be called negligible, or maybe even 0 in some exams), and are found on the electron shells and also have a charge of -1/negative. Neutrons have a mass of 1, a neutral/0 charge, and are found in the nucleus.


PLUM PUDDING MODEL

features:

  • randomly scattered electrons

  • sphere of positive charge


NUCLEAR MODEL

features:

  • mostly empty space

  • orbitals

  • electrons on orbitals

  • dense, positive nucleus


DISCOVERY OF THE ATOMS

-early 1800’s

Dalton stated that the atom is an indivisible sphere

-1897

discovery of the electron by JJ Thomson

-late 1800’s

Thomson proposed the plum pudding model

-1909

discovery of the nucleus

-1913

discovery of the electron by Niels Bohr

-next?

Rutherford proposed the nuclear model

-1917

discovery of protons by Ernest Rutherford

- Bohr’s model used electron shells and a dense positive nucleus

-1932

discovery of the neutrons by James Chadwick

-todays model of the atom


ALPHA PARTICLE SCATTERING/GOLD FOIL EXPERIMENT (RUTHERFORD)

  • started with the plum pudding model. they thought that most alpha particles would pass straight through the atom

  • more alpha particles than expected deflected which suggested that there was something in the nucleus stopping it (protons and neutrons)


ELEMENTS

mass number: number of protons + number of neutrons

atomic number: number of protons (equal to electrons)


ISOTOPES

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

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

relative atomic mass = sum of (isotope mass X abundance) / total abundance

-example

CHEMICAL AND PHYSICAL PROPERTIES

chemical property: how the substance reacts

physical property: what the substance looks like, mass, density


ELECTRONIC CONFIGURATION

group number: tells you how many electrons on the outer shell

period number: tells you the number of electron shells

-drawn and written electronic configuration


IONS and FORMING IONS

ion: an atom that has lost or gained electrons

-metals

lose electrons

form positive ions

charges:

  • group 1 = +1

  • group 2 = +2

  • group 3 = +3


-non metals

gain electrons

form negative ions

group 7 = -1

group 6 = -2

group 5 = -3


ELECTRONIC CONFIGURATION OF IONS

electronic configuration of atoms vs ions