Period 3 Cape Unit 1 Module 3 Chemistry of the elements

Period 3

CAPE UNIT 1 MODULE 3: Chemistry of the elements

Refer to Chapter 13 Chemistry for CAPE by Susan Maraj

1.1 Explain the variations in the physical properties of the elements in terms of structure and bonding

Melting point, electrical conductivity, atomic and ionic radii, electronegativity and density

Melting point

Structure and bonding

The image on the right shows the melting point trend across period 3 as well as the structure and bonding of the elements below. Na to Al are all giant solid structures with metallic bonding. Note that the melting point increases with increasing number of electrons available for delocalisation and the increasing size of the ionic charge with the smaller atomic radii for metallic bonding.Si has the highest melting point because of its giant covalent structure resembling that of diamond with a strong network of covalent bonds between Si atoms P to Cl are all simple covalent molecular structures ranging from solid to gas with weak Van derWaal's forces between the molecules or atoms. Remember the size of the molecule influences the strength of the Van der Waal's forces (P4, S8, Cl2, Ar)

ATOMIC RADIUS

CAPE uNIT 1 GUIDE

Chapter 11.2 Patterns in Period 3 elements

Atomic radius decreases across the period. As you go across the period the proton number increases so the nuclear charge increases . An extra electron is added but as all the elements are in Period 3, all the added electrons are being added to the same third shell. Electrons on the same shell exert a negligible screening or shielding effect so there is no additional shielding of outer electrons.. So the number of inner shielding electrons does not change (10 electrons) but the proton number is increasing so the atomic radius decreases as each incoming electron feels the increasing nuclear charge much stronger and are pulled closer to the nucleus

VIDEO

TRENDS IN IONIC RADII

Refer to Chapter 11.2 Patterns in period 3 elements

The ionic radii decrease from Na+ to Si4+. As we move across the period, each successive ion has one more proton in its nucleus. But electronic structure is the same. The increase in nuclear charge from Na + to Si4+ pulls the electrons closer to the nucleus. So the size of the ions decreases. A similar explanation (higher nuclear charge and same electronic structure) accounts for the decrease in ionic radius from P 3− to Cl-

VIDEO on trend in atomic radiI and ionic radiI ACROSS PERIOD 3

SUMMARY

MORE TRENDS ACROSS PERIOD 3

ELECTRICAL CONDUCTIVITY

DENSITY

ELECTRONEGATIVITY

Density depends on the mass of the atom, the size of the atoms and the way the atoms are packed together in the lattice.

The metals (Na to Al) conduct electricity well. Si is a semiconductor and the other non metals do not conduct electricity

Electronegativity increases across the period

Click the add (+) buttons below each property to learn more

trend in ionisation energy

Period 3

Generally ionisation energy ncreases across the period

There are two anomalies in this trend. The ionisation energy of Al is lower than that of Mg and the ionisation energy of S is lower than that of P. Click here for a video explaining this anomaly and also click on the + button which takes you to a link to the "Chemistry Guru"

Period 3

ionisation energy trend continued

Additionally, there is extra stability associated with a half filled subshell

1.2 describe the reactions of the elements with oxygen, chlorine and water

VIDEO

Reactions with water, oxygen and chlorine

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1.3 Describe the variation in oxidation number of oxides and chlorides

oxides and chlorides

oxidation number

The oxidation number refers to the number of valence electrons lost, gained or shared when atoms bond with each other. For the period 3 metals, the oxidation number refers to the number of valence electrons lost in ionic bonding. There is only one oxidation state for the metals. in both the oxides and the chlorides. For the period 3 non metals the oxidation state refers to the number of valence electrons shared in covalent bonding. Some of the non metals can form multiple oxidation states in their oxides and chlorides

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1.4 Describe the reactions of the oxides and chlorides with water1.5 explain the trend in the acid/base behaviour of the oxides and hydroxides

Equations are to be included

reactions of oxides with water. Click here for anothe image

Click here to see the trend in the acid /base character of the oxides and hydoxides of period 3.

reactions of chlorides with water

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1.6 predict the types of bonding present in the oxides and chlorides

VIDEO

type of bonding in period 3 oxides

Please ignore the mention of nitrogen in the video as it is not in period 3. Note the larger the electronegativity difference, the tendency will be to form ionic bonds

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Bonding in Period 3 chlorides and oxides

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1.7 Discuss the uses of some of the compounds of aluminium and phosphorous

Argon

Red and white phosphorus

Aluminiun Hydroxide

Red phosphorus is used at the side of match boxes.White phosphorus is used in flares and military applications

Aluminium hydroxide is used in antacid medication. It is basic so it would help neutrualize stomach aciidity

Argon is used in fluorescent and in incandescent lighting

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THANK YOU!

Refer to CAPE Unit 1 Guide Chapter 11

Next

This video looks at the trend in Period 2 which is the same as the trend for Period 3