Higher Chemistry: Unit 1 – Chemical Changes and Structure Part A

Higher Chemistry St. Ninian’s High School

CCS: Part A Lesson 4 – Periodicity: Electronegativity Page 1

Higher Chemistry: Unit 1 – Chemical Changes and Structure

Part A – Periodicity and Bonding

Lesson 4 – Periodicity: Electronegativity

By the end of this lesson you should know:

1. What is meant by the term electronegativity.

2. The trends in electronegativity across a period and down a group.

3. Explain the trends in electronegativity going across a period and down a group

You will have been successful in this lesson if you:

1. Read and learn the notes given

2. Complete the tasks given.

3. Complete Exercise 1.4 and check your answers.

There is also a further reading section to help you gain more depth of

understanding for this section.

MS Teams will be monitored throughout the week by a chemistry teacher. If you

need help or clarification with either the task or the content of the lesson, just

ask.

You may wish to revise the following to help you understand this lesson:

- National 5 chemistry – atomic structure, protons, electrons and electron

arrangement

Learning Outcomes

Success Criteria

Links to Prior Knowledge

For reference, the periodic table is given in the data booklet. Download or

print a copy of the Higher Chemistry Data Booklet from MS Teams or from

the SQA website -

https://www.sqa.org.uk/sqa/files_ccc/ChemistryDataBooklet_NewH_AH-Sep2016.pdf

Higher Chemistry St. Ninian’s High School

CCS: Part A Lesson 4 – Periodicity: Electronegativity Page 2

Electronegativity

It is the outer electrons in any atom which are involved in making a chemical bond

with another atom. In National 5 chemistry, you would have learned that some

atoms bond by sharing a pair of electrons, this is a called a covalent bond and

usually occurs between non-metal atoms.

The electrons in that bond are attracted to both

atoms…. but the strength of that attraction changes

depending on the atom. Some atoms have more

“pull” on the electrons that others. This is referred

to as the “Electronegativity”.

Definition: Electronegativity is a measure of the attraction an atom has for the

electrons involved in a bond.

Electronegativity values are given page 11 of the data booklet.

Notes

TASK 1 - Using the information on page 11 of the data booklet decide which

atom in the following molecules would have a greater attraction the electrons

in the bond.

1. NH

2. HF

3. CO

TASK 2 - On your data booklet, find the element with the highest

electronegativity and highlight this. Where does this element appear in the

periodic table? Now find the element with the lowest electronegativity. Where

does this element appear on the periodic table?

Higher Chemistry St. Ninian’s High School

CCS: Part A Lesson 4 – Periodicity: Electronegativity Page 3

Electronegativity: Trends

Trend in Periods:

Electronegativity increases as you go along a period due to an increase in nuclear

charge meaning the bonding electrons are held by a stronger force.

Trend in Groups:

Electronegativity decreases as you go down a group due to the atoms having more

occupied electron shells. This means:

- There is less pull on the electrons as they are increasingly further away from

nuclear attraction.

AND

- Electrons in inner shells have a screening effect shielding the bonding

electrons from nuclear attraction.

TASK 3 - Using the information on page 11 of the data booklet find the

electronegativity values for

Group 1 elements from lithium  caesium

Group 2 elements beryllium  strontium

Period 2 elements lithium  fluorine

Period 3 elements sodium  chlorine

Having gathered the data above, what general trends have you observed?

Take a moment to think about why these patterns may occur…

Sound familiar?

The explanation of the trends in electronegativity are the same as the

explanations for the trends in ionisation energy. This is because both involve

the attraction of outer electrons. The stronger the “pull” on the outer

electrons, the harder it will be for the electron to leave (ionisation energy).

Similarly the stronger the pull on the other electrons, the stronger to pull not

just on an atoms own electrons, but also on that of the other electrons in a

bond.

Higher Chemistry St. Ninian’s High School

CCS: Part A Lesson 4 – Periodicity: Electronegativity Page 4

Metals & Non-metals

Non-metals tend to have higher electronegativities than metals, because they are

on the top-right of the table.

Metals tend to have lower electronegativities than non-metals, because they are

on the lower-left area of the table.

SUMMARY

Electronegativity increases across a period due to increasing nuclear charge.

Electronegativity decreases down a group due to the atoms having more energy

levels. This means bonding electrons are further from the nuclear charge and are

shielded by inner electrons.

You should now know:

1. Atoms of different elements have different attractions for bonding electrons.

2. Electronegativity is a measure of the attraction an atom involved in a bond has

for the electrons of the bond.

3. The trends in electronegativity across periods and down groups can be

rationalised in terms of covalent radius, nuclear charge and the screening effect

due to inner shell electrons.

Learning Outcomes

Higher Chemistry St. Ninian’s High School

CCS: Part A Lesson 4 – Periodicity: Electronegativity Page 5

To learn more about electronegativity. Follow the links below:

BBC Bitesize: https://www.bbc.co.uk/bitesize/guides/zxc99j6/revision/1

Read page 8 and try the TEST

Evans2 chem web: https://www.evans2chemweb.co.uk/login/index.php#

Username: snhs password: giffnock

Select any teacher  revision material  CfE Higher  Periodicity

Royal Society of Chemistry: http://www.rsc.org/periodic-table/trends

Have a look at this periodic table, you can play around to see the periodicity

patterns in the table.

Complete Exercise 1.4 and check your answers