Discovering chemistry
Discovering chemistry

Start this free course now. Just create an account and sign in. Enrol and complete the course for a free statement of participation or digital badge if available.

Free course

Discovering chemistry

3.1 Electronegativity and the periodic table

In the last section you considered two elements, which clearly had markedly different electronegativities; chlorine, near the end of period 3, has a greater electronegativity than sodium, at the beginning.

This contrast applies generally: the electronegativities of atoms increases across a period of the periodic table; in addition electronegativities also increase up a group from the bottom to the top. This is illustrated in Figure 4. To keep things simple, only a portion of the periodic table is shown here.

Described image
Figure 4 Variation in electronegativity over the periodic table
  • Account for the variation in electronegativity shown in Figure 4. (Hint: think back to what you know about the structure of atoms).

  • Across a period of the periodic table, the atomic number, or positive charge on the nucleus, increases. This increases the attraction of the outer electrons to the nucleus, so the electronegativity of the elements also increases.

The principle quantum number of the outer electrons decreases from the bottom to the top of the group. This means that they get closer to the positively charged nucleus. The result is, again, that the outer electrons are attracted more strongly, and the electronegativity increases.

  • Suggest why the noble gases have been omitted from Figure 4

  • These are completely unreactive, in fact at normal temperatures helium, neon and argon form no compounds; hence electronegativities are not assigned to them.

So taking everything into account, top of the league table for electronegativity is fluorine, followed by oxygen and chlorine. The three most electronegative elements are shown on a green background in Figure 4.

But how does electronegativity impact on bonding?

This will be considered in the next section.


Take your learning further

Making the decision to study can be a big step, which is why you'll want a trusted University. The Open University has 50 years’ experience delivering flexible learning and 170,000 students are studying with us right now. Take a look at all Open University courses.

If you are new to University-level study, we offer two introductory routes to our qualifications. You could either choose to start with an Access module, or a module which allows you to count your previous learning towards an Open University qualification. Read our guide on Where to take your learning next for more information.

Not ready for formal University study? Then browse over 1000 free courses on OpenLearn and sign up to our newsletter to hear about new free courses as they are released.

Every year, thousands of students decide to study with The Open University. With over 120 qualifications, we’ve got the right course for you.

Request an Open University prospectus371