Atomic number, mass number and isotopes

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Structure of an atom:

The nuclear model:

Atoms contain 3 subatomic particles; protons, neutrons and electrons

The protons and neutrons are found in the nucelus(found on the center of an atom)

The nucleus is much smalller than the atom as a whole

The electrons are arranged in electron shells around the nucleus.

Protperties of sub-atomic particles:

ParticleRelative massRelative chargeProton1+1Neutron10Electron1/1836-1

The number of electrons in an atom is always the same as the number of protons, so atoms are electrically neutral overal. Atoms can lose or gain electrons: If they do, they form charged particles called ions.

Isotopes:

Atomic number and mass number:

Atomic number: The number of protons+electrons.

Atoms of a particular element all have the same number of protons

The atoms of different elements have drifferent number of protons

Mass number: The total amount of protons+neutrons

Below in chemical symbol of chlorine

The atomic number is shown below the chemical symbol(in this case, can be the other way around) and the other is the other is the atomic number

So it has...

17 protons

17 electrons

35-17=18 neutrons

Isotopes:

Atoms with the same atomic number(protons or electrons), but driffrent number of electron

Istopes have the same atomic number, but different mass number

Isotopes can be readioactive or non-reactive.

E.g. Carbon 14 is used in radiocarbon dating the age of historical objects+99Tc is used in medical imaging

Three isotopes of Hydrogen

Periodic table:

There are more than 100 drifferent elemnets.

The perodic table is a chart showing all the elments arranged in order of increasing atomic number.

Vertical collums=groups

Horizitanal rows tells us how many electrons shell their are

Periodic table=8 main groups which tells us the number of electrons in the outer shell(e.g. Group 1 elements have 1 electrons in the outer shell and Group 7 elements have 7 electrons in the outer shell)

E.g. Group 1 contains very reactive metals such as Na, while Group 7 contains very reactive non-metals such as chlorine(Cl)

No compounds in the perodic table

Electron shells:

Arranged in drifferent shells around the nucleus.

Each shell can only hold number of electrons

The innermost shell is filled first

First shell=2 max electrons

Second+Third shell=eight electrons

E.g. Litihum atom has 3 electrons. ELectron number arrangment=2,1 Carbon atom= 6 electrons=2,4

Electrons configuarations:

Electron config: a descritption of how the lectrons are arranged in an atom. It can be shown as numbers or as a diagram.

E.g. litihuium has a circle around the nucleus, with each electrons represented as a dot. The electron config for lithium is written 2,1

Electron config diagram is below