National 5 Chemistry 1.3 The Importance of Chemical Bonding Covalent Bonding in Molecules

Learning Intentions Covalent Bonding Pupils should be able to: 1.Explain why atoms combine. 2.State the diatomic elements and the types of bonds they form 3.State that the valency is the number of unpaired outer electrons 4.Calculate the valency of an element from its group number 5.State that covalent bonds form between two or more non-metal atoms forming a molecule 6.To draw how covalent bonds form by overlapping of valence electrons 7.Explain how the attraction of the positive nuclei for the shared pair of electrons holds an atom together. 8.Draw 3D molecules to demonstrate the true structure of some molecules 9.State and identify molecules with four bonds as tetrahedral in shape

Compounds like water and ammonia are made up of more than one element. If you look back to S2, what is needed to separate the elements in a compound? Answer – Energy e.g. heat or electricity! Energy is needed to separate the elements in a compound because the different atoms are JOINED TOGETHER Scientists call these join’s between atoms BONDS. Atoms are really close together and touching where there is a bond.

Covalent Bonding Non-metals atoms in molecules are joined together by COVALENT BONDS. A shorthand way is used to represent a covalent bond. A single covalent bond is shown as A double covalent bond is shown as So methane becomes

We use molimod kits to help us see these molecules and their shapes ElementColourNumber of Bonds Carbon Hydrogen Oxygen Nitrogen Sulphur Black White Oxygen Lilac Sulphur

Now it’s Your Turn In each water molecule there are _____ bonds In each ammonia molecule there are ____ bonds In each methane molecule there are ____ bonds Collect a set of Molimods and try and make the following molecules 2 3 4

CompoundChemical Formula Drawing Hydrogen Oxide Nitrogen Hydride Carbon Chloride Carbon Dioxide Carbon Hydride Chemical formula

How Does it Work? –Covalent bonding takes place between non-metals atoms only –Atoms try to attain noble gas structure by sharing electrons –The shared electrons are attracted by both nuclei and this attraction forms the covalent bond –Atoms bonded in this way form molecules

Chemical Shorthand Chemists have yet another way of representing molecules WITHOUT showing the bonds Methane's full structure becomes Formula like CH 4 and CO 2 are called the Molecular Formula This tells you the number of atoms of each element in a molecule. CH 4

CompoundChemical Formula Structural Formula Hydrogen Oxide Nitrogen Hydride Carbon Chloride Carbon Dioxide Chemical formula

Molecular Formula of Elements Most are symbol only; for example C Na S K A FEW are diatomic elements H2H2 N2N2 O2O2 F2F2 Cl 2 Br 2 I2I2 Magnificent 7!

ElementChemical Formula Type of Bond Hydrogen Oxygen Nitrogen Chlorine Diatomic Elements

Formula of Elements Most are symbol only; for example C Na S K A FEW are diatomic elements H2H2 N2N2 O2O2 F2F2 Cl 2 Br 2 I2I2

Electron Clouds and Orbitals In order to combine atoms must _______. Only the electrons are involved in bonding. Electrons are found in ________ or _______. When atoms combine they are trying to achieve the same stable electron arrangement as the ______ gases. react shells orbitals noble

Most of an atom is empty space with electrons spinning around a ___________. However although electrons are moving around they do this in a particular way. They move around in ____________ ____________. Nucleus – contains protons and neutrons 1st Energy Shell – can contain up to ___ electrons 2nd Energy Shell can contain up to ____ electrons 3rd Energy Shell can contain up to ____ electrons nucleus energy levels 2 8 8

An electron cloud or _______ is a region of space in which one or two ______ _ can be found. An electron cloud which is half-filled contains ______ electron. An electron cloud which is filled contains _______ electrons. The number of electron clouds depends on the ______ level involved. orbital electrons 1 2 energy

Energy Level Number of clouds or orbitals Max Number of Electrons Add this table into your notes

Outer –Electron Pictures Since it is the _______________ of atoms that meet when they join, the key to understanding how and why they do this is the _____________ of ________ electrons in each atom. This depends only on the _____________ of outer electrons, the _____________ number of the element, since electrons are assigned to ___________ according to fixed _____________. Thus all elements in the same ____________ have identical ___________ electron _____________ and can be distinguished only by including the element ______________. Barium; Group 2 Tellurium; Group 2 electrons numberouter number atomic orbital's shells groupouter numbers symbol

Draw the atoms: hydrogen, carbon, nitrogen and chlorine

Complete the table below in your notes Element HydrogenCarbonNitrogenOxygenFluorine Electron Arrangement 12,6 Number of electrons needed to fill the outer shell 12 Valency 12 Element SiliconPhosphor us SulphurChlorine Electron Arrangement 2,8,5 Number of electrons needed to fill outer shell 3 Valency 3

Hydrogen Molecule H 2 This is often shown as: H Where represents a covalent __________ i.e. a ___________ _________ of electrons. bond shared pair

Nitrogen HydrideSulfur hydride Carbon Dioxide Carbon Chloride

Atoms Sharing Electrons The following dot-and-cross diagrams show how atoms combine covalently to form a: Fluorine molecule Fluorine atoms share their ___________ electrons such that each atom has the stable arrangement of the noble gas __________. outer neon

Chlorine has atomic number 17 It has 17 protons in its nucleusIt also has 17 electrons 2 in the inner shell8 in the next shell7 in the outer shell Chlorine We need 2 chlorine atoms These atoms can then share electrons to complete their outer shells A chlorine molecule is formed Also written Cl-Cl or Cl 2

Oxygen has atomic number 8 Therefore it has 8 electrons 2 in the inner shell 6 in the outer shell We need a second oxygen To complete the outer shell, they each need to share 2 electrons, so a total 4 electrons are shared The covalent bonds can be shown like this. Or like this O=O

Oxygen molecule Oxygen atoms share their ________ electrons such that they have stable arrangements of the noble gas _________. outer neon

2. Covalent bonds- Two atoms share one or more pairs of outer- shell electrons. Oxygen Atom Oxygen Molecule (O 2 ) Oxygen Molecule (O 2 )

Nitrogen molecule linear, angular, trigonal pyramidal and tetrahedral. Nitrogen atoms share their ________ electrons such that they have stable arrangements of the noble gas __________. outer neon

Any attractive force that causes atoms to “stick” together is called a bond. When neutral atoms share electrons the attractive force is called a covalent bond. A covalent bond is the electrostatic attraction between a shared pair of negatively charged electrons and the two positively charged nuclei of the atoms sharing these electrons. This is a very strong attraction.

Shapes of Molecules NameModelFormulaDescription of Shape HydrogenH2H2 Hydrogen Chloride Water Nitrogen Hydride Methane (Carbon Hydride) Linear

Methane CH 4

Carbon has atomic number 6 It therefore has 6 electrons 2 in the inner shell 4 in the outer shell Hydrogen has just one electron And we need 4 hydrogens Now both carbon and all 4 hydrogens have complete outer shells 4 covalent bonds have been made Covalent bonds can be shown like this. Or like this

2 Chlorine Cl 2 Iodine I 2 Carbon Dioxide CO 2 Water H 2 O Most covalent compounds have small molecules. They are gases, Liquids or solids with low melting & boiling points.