The Structure of the Atom

The atom is composed of a negative, positive and neutral charge

Na

Nucleus

Electrons

They are very, very tiny so the atom is mainly empty space. Electrons have a negative charge

Shells

The first shell always contains two electrons when full whereas the other shells have a maximum of eight electrons

The nucleus contains protons which have a positive charge. It also contains neutrons which have no charge

*Na being sodium with this particular atomic structure.

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How atoms combine

Ionic bonding

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WHY DO COMPOUNDS FORM IN THE FIRST PLACE?

Scientists found that elements in Group 8 were very non-reactive.

They also noticed that those in Groups 1,2,6 and 7 were extremely reactive.

They also noticed that metallic substances had several properties that were very different from other elements.

They could not at first understand why.Eventually they discovered that it had to do with

ELECTRON CONFIGURATIONS and

STABILITY

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ELECTRON CONFIGURATION AND STABILITY

Scientists’ research showed that in compounds,

elements will combine so that the valence or

outermost electrons will have the same electron

configuration as the nearest noble gas

(in Group 8)

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HOW CAN ELEMENTS COMBINE TO ACHIEVE THIS?

There are

three (3) ways

An element can lose electrons to another element to have the

same electron configuration as the nearest noble gas. Once an atom loses

one or more electrons, it forms a positively charged particle known as a

CATION.

An element can gain electrons from the element it combines with to have the same electron configuration as

the nearest noble gas. Once an atom gains one or more

electrons, it becomes a negatively charged particle known as an ANION

An element can share valence electrons with

another element to have the same

electron configuration as the nearest noble gas.

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YOU MAY WELL BE ASKING

WHAT DOES THIS MEAN?

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LET’S TAKE A LOOK AT SOME EXAMPLES TO UNDERSTAND THIS CONCEPT MORE FULLY

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Prepared by JGL 8/21/20098

Sodium’s atomic number is Z=11. Its

electron configuration is therefore 2,8,1

Neon’s atomic number is Z=10. Its

electron configuration is 2,8. It is the

nearest noble gas to sodium.

Sodium will combine with another element so that it can change its electron configuration from 2,8,1 to 2,8. To do this, it must lose 1

electron and give it to the element with which it combines.

Let’

s t

ake s

od

ium

as a

n

exam

ple

9

Chlorine’s atomic number is Z=17. Its

electron configuration is therefore 2,8,7

Argon’s atomic number is Z=18. Its

electron configuration is 2,8,8. It is the

nearest noble gas to chlorine.

Chlorine will combine with another element so that it can change its electron configuration from 2,8,7 to 2,8,8. To do this, it must gain 1

electron from the element with which it combines.

Let’

s t

ake c

hlo

rin

e a

s a

n

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ple

Ionic bonding

It only occurs between a metal and a non-metalIt is formed from an attraction between positively charged

and negatively charged ionsIonic bonding involves the complete transfer of electrons

from one atom to anotherThis means that elections will try to fill an empty shell of an

atom using the minimum amount of energy. So if there are 7 in one outer shell and 1 in the other, the atom with 1 will lose its electron and the one with 7 will gain it

Remember that when an atom loses an electron it becomes positively charged [e.g. 1+] whereas the atom which gains an electron becomes negatively charged [e.g. 1-]

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Ionic bonding examplee.g. Sodium chloride. Remember to draw all the shells in an exam unless it asks for just the outer shell as it may lose you marks

Na

Na

Cl

Cl

1+1-

ION

IC B

ON

DIN

G O

F S

OD

IUM

CH

LO

RID

E

In order to form the compound sodium chloride, there are three (3) steps.

First, the sodium atom loses one electron to form a positive sodium ion. (cation)

Then the chlorine atom accepts the electron from the sodium atom to form a negative chloride ion (anion).

Then the sodium cation and chloride anion become attracted to each due to their different charges, forming an ionic bond

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IONS DEFINED

An ion is an atom or molecule where the total

number of electrons is not equal to the total number of protons, giving it a net

positive or negative electrical charge.

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REVIEW – ELECTRON CONFIGURATIONS

What is an electron configuration?

How do we represent electron configurations?

Definition: Electron configuration is the arrangement of electrons in an atom, molecule or other body.

By using Bohr-Rutherford diagrams

11 p10 n

Or electron configuration notation

2,8,1

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LET’S CONTRAST –FLOURINE AND NEON

Element symbol F Group 17 Atomic Number Z = 9 Mass number A = 19 Electron configuration:

2,7 Bohr-Rutherford diagram

Element symbol Ne Group 18 Atomic Number Z = 10 Mass number A = 20 Electron configuration:

2,8 Bohr-Rutherford

diagram

Fluorine Neon

9 p10 n

10 p10 n

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REMEMBER – “CONTRAST” MEANS “LOOK AT THE DIFFERENCES”

LET’S CONTRAST – SODIUM AND NEON

Element symbol Na Group 1 Atomic Number Z = 11 Mass number A = 23 Electron configuration:

2,8,1 Bohr-Rutherford diagram

Element symbol Ne Group 18 Atomic Number Z = 10 Mass number A = 20 Electron configuration:

2,8 Bohr-Rutherford

diagram

Sodium Neon

10 p10 n

11 p12 n

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COMPARE AND CONTRAST ALL 3 ELEMENTS

F and Ne have the same number of electron shells

Different atomic numbers (Z) and therefore protons

Different mass numbers (A) and therefore different neutrons

F needs to gain 1 electron to have the same number of electrons as Ne

Na needs to lose 1 electron to have the same number of electrons as Ne

Similarities Differences

Scientists found that when elements from Group 1 and Group 7 combine, they lose or gain an electron to have

the same number of electrons as the nearest

Noble Gas.

i.e. F and Na form ions that are ISO-

ELECTRONIC with Ne

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Remember – “Compare”

means “Look at

IN GENERAL

To become ISO-ELECTRONIC with the nearest Noble Gas (either within the same Period or the Period just above)

1. Group 1 elements lose 1 e-2. Group 2 elements lose 2 e-3. Group 3 elements lose 3 e-

This only happens when combining or reacting with another element(s) from Groups 15,16 or 17

To become ISO-ELECTRONIC with the nearest Noble Gas (either within the same Period or the Period just above)

1. Group 15 elements gain 3 e-2. Group 16 elements gain 2 e-3. Group 17 elements gain 1 e-

This only happens when combining or reacting with another element(s) from Groups 1,2 or 3

Groups 1, 2 and 3 Groups 15, 16 and 17

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