3c. Electron configuration, elements in the periodic table forming covalent bonds - covalent compounds

Which elements from the periodic table combine to form covalently bonded molecules?

Its a good idea to have some idea of where the elements are in the periodic table, and their electronic structure, before looking at the theoretical electronic model for covalent bonding in molecules (elements or compounds).

The black zig–zag line 'roughly' divides the metals on the left from the non–metals on the right of the elements of the Periodic Table - combining elements on the right usually results in a covalent bond.

The electronic structures of the first 20 elements of the Periodic Table You need to know these to understand the details of covalent chemical bonding and working out dot and cross electronic diagrams of molecules (GCSE level)

Pd metals Part of the modern Periodic Table Pd = period, Gp = group metals => non–metals Gp1 Gp2 Gp3 Gp4 Gp5 Gp6 Gp7 Gp0 1 1H  Note that H does not readily fit into any group 2He 2 3Li 4Be atomic number Chemical Symbol eg 4Be 5B 6C 7N 8O 9F 10Ne 3 11Na 12Mg 13Al 14Si 15P 16S 17Cl 18Ar 4 19K 20Ca 21Sc 22Ti 23V 24Cr 25Mn 26Fe 27Co 28Ni 29Cu 30Zn 31Ga 32Ge 33As 34Se 35Br 36Kr 5 37Rb 38Sr 39Y 40Zr 41Nb 42Mo 43Tc 44Ru 45Rh 46Pd 47Ag 48Cd 49In 50Sn 51Sb 52Te 53I 54Xe 6 55Cs 56Ba Transition Metals 81Tl 82Pb 83Bi 84Po 85At 86Rn Gp 1 Alkali Metals  Gp 2 Alkaline Earth Metals  Gp 7 Halogens  Gp 0 Noble Gases Chemical bonding comments about the selected elements highlighted in white Two of the highlighted non–metals on the right of the periodic table (and hydrogen) may combine with each other OR with themselves. In doing so, covalent bonds are formed, e.g. the formation of a covalent compounds like hydrogen chloride gas HCl, sulfur dioxide gas SO2, liquid water H2O, and element molecules like hydrogen H2 or oxygen O2.

A bigger picture, but not exclusively is shown below

Pd

metals

Part of the modern Periodic Table Pd = period, Gp = group

metals => non–metals

Gp1

Gp2

Gp3

Gp4

Gp5

Gp6

Gp7

Gp0

1

1H  Note that hydrogen does not readily fit into any group but is a non-metal

2He

2

3Li

4Be

atomic number Chemical Symbol eg 4Be

5B

6C

7N

8O

9F

10Ne

3

11Na

12Mg

13Al

14Si

15P

16S

17Cl

18Ar

4

19K

20Ca

21Sc

22Ti

23V

24Cr

25Mn

26Fe

27Co

28Ni

29Cu

30Zn

31Ga

32Ge

33As

34Se

35Br

36Kr

5

37Rb

38Sr

39Y

40Zr

41Nb

42Mo

43Tc

44Ru

45Rh

46Pd

47Ag

48Cd

49In

50Sn

51Sb

52Te

53I

54Xe

6

55Cs

56Ba

Transition Metals

81Tl

82Pb

83Bi

84Po

85At

86Rn

The non-metals in the Periodic Table highlighted in white, tend to form covalent bonds with each other (for GCSE level). This might be as an element or a compound, usually forming small molecules, but sometimes a giant structure (e.g. B, C and Si)

Most covalent molecules you will come across are formed by combinations of atoms of non–metallic elements on the right–hand side of the Periodic Table eg

from Group 4 carbon and silicon, from Group 5 nitrogen and phosphorus and from the Group 7 Halogens – fluorine, chlorine, bromine and iodine.

Hydrogen also forms predominantly covalent compounds and so does the Noble Gas xenon in Group 0.

Don't forget, even non–metal elements can form molecules eg hydrogen H₂ and phosphorus P₄.

Brief summary of the Periodic Table including electronic structure and formula patterns

You should be able to from Parts 3 and 4:

know when atoms share pairs of electrons, they form strong covalent bonds,

covalently bonded substances may consist of small molecules. and recognise common substances that
consist of small molecules from their chemical formula,

know that some covalently bonded substances have very large molecules, such as polymers,

know that some covalently bonded substances have giant covalent structures such as diamond and silicon dioxide,

appreciate that covalent bonds in molecules and giant structures can be represented in various forms

draw dot and cross diagrams for the molecules like hydrogen, chlorine, oxygen, nitrogen, hydrogen chloride, water, ammonia and methane,

represent the covalent bonds in small molecules, in the repeating units of polymers and in part of giant covalent structures, using a line to represent a single bond,

describe the limitations of using dot and cross, ball and stick, two and three-dimensional diagrams to represent molecules or giant structures,

deduce the molecular formula of a substance from a given model or diagram in these forms showing the atoms and bonds in the molecule.

Be able to define empirical formula and molecular formula

Be able to calculate empirical and molecular formula from given data

Key points about the location of covalent-bonding elements

• Covalent bonds form between non-metal atoms.
• Periodic table regions:
  • Found on the right-hand side of the periodic table (Groups 4, 5, 6, 7).
  • Includes Hydrogen (Group 1, but behaves like a non-metal).
  • Common non-metals: Carbon, Nitrogen, Oxygen, Fluorine, Chlorine, Sulfur, Phosphorus, Hydrogen.
• Metalloids (e.g. Silicon) can also form covalent bonds.
• Metals (left-hand side) generally form ionic or metallic bonds, not covalent.

Typical Exam Board Requirements

Student Exam Tips

• Look at periodic table position:
  • Metals (left) → ionic/metallic bonding.
  • Non-metals (right) → covalent bonding.
• Memorise key non-metals: H, C, N, O, F, Cl, S, P.
• Check bonding partners:
  • Non-metal + non-metal → covalent.
  • Metal + non-metal → ionic.
• Practice examples:
  • H₂, O₂, N₂, H₂O, HCl, CH₄, CO₂, NH₃, Cl₂.
• Exam technique:
  • Use the phrase “non-metals share electrons to form covalent bonds.”
  • Be ready to explain why metals don’t form covalent bonds.

Typical Misconceptions

• “Metals form covalent bonds” → Incorrect. Metals form metallic bonds or ionic bonds with non-metals.
• “Hydrogen is a metal” → False. Hydrogen behaves as a non-metal in bonding.
• “Group number = valency always” → Not strictly true; e.g. Oxygen (Group 6) has valency 2.
• “All non-metals form ionic bonds” → Wrong. Non-metals with other non-metals form covalent bonds.
• “Covalent bonds are weak” → Misleading. Covalent bonds are strong; weak forces exist between molecules.

Quick Revision Overlay

• Where to find covalent bond formers: Right-hand side of periodic table (Groups 4–7 + hydrogen).
• Bond type: Non-metal + non-metal → covalent.
• Examples: H₂, O₂, N₂, H₂O, HCl, CH₄, CO₂, NH₃, Cl₂.
• Exam focus: Identify non-metals, predict bonding type, explain properties.