C3 Atoms, elements & compounds

C3 Atoms, elements & compounds 3.5: Molecules & Covalent bonds 3.6: Giant Structures Req-giant structure

3.5: Learning Objectives • State that non-metallic elements form non-ionic compounds using a different type of bonding called covalent bonding. • Describe the differences in volatility, solubility and electrical conductivity between ionic & covalent compounds. (H/W)

3.5: Learning Objectives • Supplement: • Draw dot-and-cross diagrams to represent the sharing of electron pairs to form single covalent bonds in simple molecules, exemplified by Cl2, H2O, CH4, HCl. • Draw dot-and-cross diagrams to represent the multiple bonding in N2, C2H4 & CO2

Cl Cl H (1) (2,8,7) H (2) (2,8,8) Covalent bonding in hydrogen chloride Both hydrogen (1) and chlorine (2.8.7) needs 1 more electron to attain a full outer shell. H-Cl

(H) Draw dot and cross diagrams for the following molecules and check your answers with the following slides (right click to zoom) N2, C2H4 N2, C2H4 N2 C2H4

Atom Molecule Formula O O O N N N H H H P P P P P Chemical formula of elements • Each element has a symbol. • Some elements exist as particular numbers of atoms bonded together. • This fact can be represented in a formula with a number which shows how many atoms. O2 N2 H2 P4

Name Formula Methane H H C H H Carbon dioxide O O C Water H O H The formula of molecular compounds • Molecular compounds have formulae that show the type and number of atoms that they are made up from. CH4 CO2 H2O

1. Octane • The molecular formula of this compound: • The number of different elements present in this compound: • Names of each element and how many atoms of each element:

2. Propane • The molecular formula of this compound: • The number of different elements present in this compound: • Names of each element and how many atoms of each element:

3. Ethanoic acid • The molecular formula of this compound: • The number of different elements present in this compound: • Names of each element and how many atoms of each element:

4. Hydrogen peroxide • The molecular formula of this compound: • The number of different elements present in this compound: • Names of each element and how many atoms of each element:

4. Ethene • The molecular formula of this compound: • The number of different elements present in this compound: • Names of each element and how many atoms of each element:

5. Methanol • The molecular formula of this compound: • The number of different elements present in this compound: • Names of each element and how many atoms of each element:

4.1

20.08.12 Bonding Answer the questions below • Write down the formula that contains 4 elements. • Write down the formula that is made up of 5 atoms. • Write down the formula that is a hydrocarbon. • Write down the formula that is made up of two elements and two atoms in total

Basic ideas- match up

3. Ethanoic acid • The molecular formula of this compound: • The number of different elements present in this compound: • Names of each element and how many atoms of each element:

4. Hydrogen peroxide • The molecular formula of this compound: • The number of different elements present in this compound: • Names of each element and how many atoms of each element:

4. Ethene • The molecular formula of this compound: • The number of different elements present in this compound: • Names of each element and how many atoms of each element:

5. Methanol • The molecular formula of this compound: • The number of different elements present in this compound: • Names of each element and how many atoms of each element:

C3: Covalent bonding Non-metals combine together by sharing electrons and this is called covalent bonding

How is HCl bonded? • HCl

Covalent compounds • Covalent compounds are formed when non-metal atoms react together. • As these atoms come near their outer electrons are attracted to the nucleus of both atoms and become shared by the atoms. • The shared electrons count towards the shells of both atoms and therefore help fill up incomplete electron shells. (Duplet 2 ) (Octet 8)

- Figure 1 Figure 2 F F X X F F Covalent bonds • Covalent compounds are held together by this sharing of electrons. • A pair of electrons shared in this way is known as a covalent bond. • It is sometimes represented in full bonding diagrams (see figure 1). Often these bonds are just shown as a pair of electrons (xx) or even just a line (see figure 2).

(H) Draw dot and cross diagrams for the following molecules and check your answers with the following slides (right click to zoom)

3.5: Learning Objectives • Supplement: • Draw dot-and-cross diagrams to represent the sharing of electron pairs to form single covalent bonds in simple molecules, exemplified by Cl2, H2O, CH4, HCl. • Draw dot-and-cross diagrams to represent the multiple bonding in N2, C2H4 & CO2

HCl. • Cl2 • H2O, • CH4 • N2 • C2H4 • CO2

Ionic & covalent bonding • When an atom of a metal joins with an atom of a non-metal an ionic bond is formed. • When 2 non-metals combine they share electrons to form a covalent bond. The atoms join to form a molecule.

Covalent Bonding • This involves electrons being shared • Full outer shells are formed. • Resulting in a stable structure • Covalent bonds are made between atoms of non-metals • Examples of molecules with covalent bonds include: Water and Carbon dioxide

Basic ideas • Elements are chemically joined to make ………….. • The connection between the atoms in a compound is called a …………….. bond • There are two types of this: ……………… bonding and ...………… bonding • The type of chemical bonding between metals and non-metals is ……………. and the type of chemical bonding between non-metals is ………………… • A substance that is made of two or more atoms bonded together is called a m……………..

Basic ideas • Elements are chemically joined to make compound • The connection between the atoms in a compound is called a chemical bond • There are two types of this: covalent bonding and ionic bonding • The type of chemical bonding between metals and non-metals is ionic and the type of chemical bonding between non-metals is covalent • A substance that is made of two or more atoms bonded together is called a molecule

C3: Covalent bonding Non-metals combine together by sharing electrons and this is called covalent bonding

Covalent compounds • Covalent compounds are formed when non-metal atoms react together. • As these atoms come near their outer electrons are attracted to the nucleus of both atoms and become shared by the atoms. • The shared electrons count towards the shells of both atoms and therefore help fill up incomplete electron shells. (Duplet 2 ) (Octet 8)

- Figure 1 Figure 2 F F X X F F Covalent bonds • Covalent compounds are held together by this sharing of electrons. • A pair of electrons shared in this way is known as a covalent bond. • It is sometimes represented in full bonding diagrams (see figure 1). Often these bonds are just shown as a pair of electrons (xx) or even just a line (see figure 2).

(H) Draw dot and cross diagrams for the following molecules and check your answers with the following slides (right click to zoom)

H H (1) (1) H (2) Covalent bonding in hydrogen – H2 Hydrogen (1) needs 1 more electron to attain a full outer shell. H-H H (2)

Cl Cl Cl (2,8,7) (2,8,7) Cl (2,8,8) (2,8,8) Covalent bonding in chlorine Cl2 Chlorine (2.8.7) needs 1 more electron to attain a full electron shell. Cl-Cl

H H H H H H H H C C 4 • How many does carbon (2,4) need? 4 • How many hydrogens per 1 carbon? • Hydrogen (1) needs 1 more electron. • Draw bonding diagrams for methane – CH4.

Covalent bonding in Carbon dioxide – CO2 Carbon needs 4 more electrons but oxygen (2.6) needs 2 more. Therefore, we need 2 oxygen's. O C O 4 electrons: Double covalent bond 4 electrons: Double covalent bond Represented as = O C O

O O H H H H H H O Covalent bonding in water – H2O Hydrogen (1) needs 1 more electron but oxygen (2.6) needs 2 more. Therefore, we need 2 hydrogen's.

Cl-Cl O=O N=N Double bond Triple bond Single bond Covalent bonding - multiple bonds • Mostly electrons are shared as pairs. • There are some compounds where they are shared in fours or even sixes. • This gives rise to single, double and triple covalent bonds. • Again, each pair of electrons is often represented by a single line when doing simple diagrams of molecules.

Task • Can you draw a dot and cross diagram for Oxygen • Nitrogen • Ethene C2H4 • HCl

O O O O Covalent bonding in oxygen Oxygen (2.8.6) needs 2 more electrons to attain a full electron shell. O=O 4 electrons

N=N N N N N Nitrogen (Higher) Nitrogen (2.8.5) needs 3 more electrons to attain a full electron shell and forms a triple bond. Draw a bonding diagram of nitrogen. 6 electrons

Supplement • Ensure you can draw structures for the following: • Remember the exam is not restricted to using only these! So practice and ensure you understand this! • Chlorine • Water • Methane • Hydrogen Chloride • Nitrogen • Ethene • Carbon Dioxide

Covalent bonding animation • sc_ocr_c3c2

Draw ‘dot and cross’ type bonding diagrams for each of the following: H H F H O C O C C H H S H H H H • Hydrogen fluoride (HF) • Hydrogen sulphide (H2S) • Ethane (C2H6 and the carbons are joined by a single covalent bond) • Carbon dioxide (CO2 and the carbon oxygen bonds are double bonds)

C3 Atoms, elements & compounds