1.3 Atomic Structure

8/2/2019 1.3 Atomic Structure

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Atomic Structure


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The atom is the smallest part of an element thatstill has the properties of the element.

Composed of 3 types of sub-atomic particles: Protons, neutrons, and electrons.

Mostly empty space (domain of electrons).

Most of the mass collected in a very tiny nucleus(neutrons & protons).

Nucleus has a positive charge due to protons, butthe atom as a whole is neutral.


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Protons, neutronsand electrons all havesignificant effects ona an atoms stabilityand reactivity.

Atomic notationallows for quickreference of all thesubatomic parts of anatom.

Particle Symbol Charge Mass(kg)

Location

Proton p+ 1+ 1.67 X 10-27 nucleus

Neutron n0 0 1.67 X 10-27 nucleus

Electron e- 1- 9.11 X 10-31 Outsidenucleus


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Electrons: occupy specific energy levels. have less energy in levels closest from the

nucleus due to the strong attraction tothe positive nucleus, more energy fartheraway.

Maximum number of electrons perenergy level is:Period 1 - 2 e- (closest to nucleus)Period 2 - 8 e-Period 3 - 8 e-

Note: beyond calcium the pattern is morecomplicated).


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Represents the number of protons in an atom ofa particular element.

Can be used to identify and specify the element.(The proton is the unit of matter!)

Elements are arranged in the periodic table inorder of increasing atomic number

eg. Li has 3 protons, C has 6, Cl has 17

* In each atom, the number of protons equals the number ofelectrons. (Atoms are generally neutral!)


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Is the number of protons & neutrons in an atom. Only protons and neutrons have significant mass in the

atom. The electrons mass is so small it is ignored in theatomic mass number.

eg. Li mass number = 6.94 (rounded to 7)

To determine the number of neutrons in an atomicnucleus, subtract atomic number from atomic mass.

eg. Li Atomic mass = 7Atomic number = 3

Neutrons = 4


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Atoms of the same element that containdifferent numbers of neutrons, therefore havingdifferent masses.

Remember that atoms of the same element

have the same atomic number the samenumber of protons.

eg. Hydrogen:


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For an atom, electrons fill up lower energylevels first, moving up levels until all electronsare placed.


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Elements in the same family/group have thesame reactivity. This is related to the number of

electrons in the outer shell, called valence.Valence electrons are the electrons in the outer

shell.


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Octet Rule : states that atoms bond in such away as to have 8 electrons in their outer shell,full like a noble gas! Exceptions are H, Li, Bewho need only 2 like He

Practice Question:

For the following elements:

1) State the number of protons, neutrons, and electrons

2) State the number of occupied energy levels in the atom3) State the number of valence electrons

a) sodium b) flourine c) barium d) xenon


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Period Number is relevant as it tells the number of energylevels required to support all the electrons in an atom.

Group Number tells us the number of valence electrons inthe outer energy level of an atom.

This is most easily recognized in the A group numbers.

Eg. alkali : valence of 1

alkaline earth : valence of 2halogens : valence of 7noble gases : valence of 8 full outer shell,

very stable/unreactive

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1.3 Atomic Structure