The Structure of the Atom The atom is composed of a negative, positive and neutral charge Na Nucleus...
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Transcript of The Structure of the Atom The atom is composed of a negative, positive and neutral charge Na Nucleus...
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
exam
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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