# Periodic Table: Trends in Electronegativity of Elements Chemistry Tutorial

## Key Concepts

• In 1932 Linus Pauling defined electronegativity as the power of an atom in a molecule to attract electrons to itself.
• Pauling devised a numerical electronegativity scale, based on bond energies.
• In general, electronegativities decrease down a Group of the Periodic Table.
• In general, electronegativities increase going from left to right across a Period of the Periodic Table.1

 electronegativity increases across a period from left to right smallest → → → → largest electronegativity decreases down a group from top to bottom largest Li Be B C N O F ↓ Na Mg Al Si P S Cl ↓ K Ca Ga Ge As Se Br ↓ Rb Sr In Sn Sb Te I smallest Cs Ba Tl Pb Bi Po At

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## Trends in Electronegativities in Groups of the Periodic Table

In general, the electronegativities of the elements in a Group of the periodic table decrease as you go down the group from top to bottom.

As the atomic radius2 increases and the number of completed electron shells ( energy levels) increases going down the group, the power of the atom's nucleus to attract electrons to itself decreases.

Group Atomic Radius Trend Electronegativity Trend
top element period 2 element smallest most electronegative
period 3 element
period 4 element
period 5 element
bottom element period 6 element largest least electronegative

We will consider the trends in the electronegativity of group 1 elements and group 17 elements in the sections below.

### (A) Trends in the Electronegativity of Group 1 (IA, Alkali Metals) Elements

Consider the data for the elements of group 1 in the table below.

Can you see a pattern (trend) in the size of the atoms and their electronegativity?

Element Atomic Number(Z) Symbol Atomic Radius (pm)3 Electronegativity Trend lithium 3 Li 134 0.98 most electronegative ↓ sodium 11 Na 154 0.93 ↓ potassium 19 K 196 0.82 ↓ rubidium 37 Rb 211 0.82 ↓ cesium 55 Cs 225 0.79 ↓ least electronegative

Did you notice that as you go down the group from top to bottom:

• Atomic radius increases (from 134 pm for Li to 225 pm for Cs)
• Electronegativity decreases (from 0.98 for Li to 0.79 for Cs)

As the atomic radius increases and the number of completed electron shells ( energy levels) increases going down the group, the power of the atom's nucleus to attract electrons to itself decreases.

### (B) Trends in the Electronegativity of Group 17 (VIIA, Halogens) Elements

Consider the data for the elements of group 17 in the table below.

Can you see a pattern (trend) in the size of the atoms and their electronegativity?

Element Atomic Number(Z) Symbol Atomic Radius (pm) Electronegativity Trend fluorine 9 F 71 3.98 most electronegative ↓ chlorine 17 Cl 99 3.16 ↓ bromine 35 Br 114 2.96 ↓ iodine 53 I 133 2.66 ↓ lowest electronegativity

Did you notice that as you go down the group from top to bottom:

• Atomic radius increases (from 71 pm for F to 133 pm for I)
• Electronegativity decreases (from 3.98 for F to 2.66 for I)

As the atomic radius increases and the number of completed electron shells ( energy levels) increases going down the group, the power of the atom's nucleus to attract electrons to itself decreases.

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## Trends in Electronegativity of the Elements in Periods of the Periodic Table

In general, electronegativities of the elements in the same Period increases as you go from left to right across the period.

As the nuclear charge increases and the atomic radius decreases across a period, the power of the atom's nucleus to attract electrons to itself increases.

 atomic radius decreases across a period from left to right largest atom → → → smallest atom a period Group 1element Group 2element Group 13element Group 14element Group 15element Group 16element Group 17element lowest electronegativity → → → highest electronegativity electronegativity increases across a period from left to right

In the next section we will look at the trends in the electronegativities of elements in period and period 3 of the periodic table.

### (A) Trends in the Electronegativity of Elements in Period 2 of the Periodic Table

Consider the data in the table below for elements in period 2 of the periodic table.

Can you see any patters (trends) in

• electronegativity

 Element Atomic Number (Z) Atomic Radius (pm) Electronegativity General Trend Li Be B C N O F 3 4 5 6 7 8 9 134 90 82 77 75 73 71 0.98 1.57 2.04 2.55 3.04 3.44 3.98 leastelectronegative → → → → → mostelectronegative

Did you notice that as you go across period 2 from left to right

• atomic radius decreases (from 134 pm for Li to 71 pm for F)
• electronegativity increases (from 0.98 for Li to 3.98 for F)

As the nuclear charge increases and the atomic radius decreases across a period, the power of the atom's nucleus to attract electrons to itself increases.

### (B) Trends in the Electronegativity of Elements in Period 3 of the Periodic Table

Consider the data in the table below for elements in period 3 of the periodic table.

Can you see any patters (trends) in

• electronegativity

 Element Atomic Number (Z) Atomic Radius (pm) Electronegativity General Trend Na Mg Al Si P S Cl 11 12 13 14 15 16 17 154 130 118 111 106 102 99 0.93 1.31 1.61 1.9 2.19 2.58 3.16 leastelectronegative → → → → → mostelectronegative

Did you notice that as you go across period 3 from left to right

• atomic radius decreases (from 154 pm for Na to 99 pm for Cl)
• electronegativity increases (from 0.93 for Na to 3.16 for Cl)

As the nuclear charge increases and the atomic radius decreases across a period, the power of the atom's nucleus to attract electrons to itself increases.

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## Problem Solving using StoPGoPS method

Question:

Consider the main group elements W, X, Y and Z located in the periodic table as shown below:

 W X Y Z

Which of these elements, W, X, Y or Z, would be the most electronegative?

 STOP STOP! State the Question. What is the question asking you to do? Determine which is the most electronegative element. PAUSE PAUSE to Prepare a Game Plan (1) What information (data) have you been given in the question? (a) The symbols for four unknown elements: W, X, Y and Z (b) Location of the four elements in the periodic table: W: group 16 period 2 X: group 2 period 3 Y: group 16 period 4 Z: group 2 period 5 (2) What is the relationship between what you know and what you need to find out? (a) electronegativity decreases down a group from top to bottom (b) electronegativity increases across a period from left to right GO GO with the Game Plan (a) electronegativity decreases down a group from top to bottom (i) Group 16: W is more electronegative that Y (ii) Group 2: X is more electronegative than Z (iii) Group 2: the unlabelled group 2 element above X in period 2 is more electronegative than X (b) electronegativity increases across a period from left to right (i) The unlabelled group 2 element above X in period 2 is less electronegative than W (ii) Since X is less electronegative than the unlabelled element above X, it follows that W is the most electronegative element of these four elements. PAUSE PAUSE to Ponder Plausibility Is your answer plausible? Group 2 elements are metals more likely to lose an electron to form a positive ion, therefore not very electronegative. The elements at the top of group 16 are non-metals which are more likely to attract electrons towards them and are therefore more electronegative. Elements at the bottom of group 16 are more metallic and so are less electronegative than the elements at the top of the group. This means that W is the most non-metallic element present, and therefore the most electronegative. Since this agrees with the answer we got above, we are reasonably confident that our answer is plausible. STOP STOP! State the Solution W is the most electronegative of these four elements.

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Footnotes

1. We will be excluding transition metals, lanthanoids (lanthanides) and actinoids (actinides) from the disucssion

2. The values for atomic radii provided here are approximations derived from interatomic-distance measurements.
There are a number of different ways of approaching the measurement of atomic and ionic radii. We are not going to discuss any of them, we are just going to use some nicely behaved approximations to illustrate some general trends.

3. Common units for the reporting of atomic radii are the picometre (as used here), the nanometre, and the angstrom.
1 pm = 1 picometre = 10-12 metre
1 Å = 1 angstrom = 10-10 metre
1 nm = 1 nanometre = 10-9 metre
Conversion example for the atomic radius of lithium,
134 pm = 134 × 10-12 m = 0.134 × 10-9 m = 0.134 nm
134 pm = 134 × 10-12 m = 1.34 × 10-10 m = 1.34 Å