CHARACTERISTICS PROPERTIES OF TRANSITION ELEMENTS

 Subject: 

CHEMISTRY

Term:

FIRST TERM

Week:

WEEK 7

Class:

SS 2

Topic:

CHARACTERISTICS PROPERTIES OF TRANSITION ELEMENTS

 

Previous lesson: 

The pupils have previous knowledge of

 IONIC THEORY

that was taught as a topic in the previous lesson

 

Behavioural objectives:

At the end of the lesson, the learners will be able to

• State the Meaning of Electrolysis
• Express the Definition of various Terms
• Explain Preferential Discharge of Ions during Electrolysis

 

 

Instructional Materials:

• Wall charts
• Pictures
• Related Online Video
• Flash Cards

 

 

Methods of Teaching:

• Class Discussion
• Group Discussion
• Asking Questions
• Explanation
• Role Modelling
• Role Delegation

 

Reference Materials:

• Scheme of Work
• Online Information
• Textbooks
• Workbooks

 

CHARACTERISTICS PROPERTIES OF TRANSITION ELEMENTS

1. Paramagnetism: Transition elements exhibit paramagnetism because of the presence of unpair elecrons in the d-orbital. Paramagnetism is the ability of an element to align to the poles of a magent.
2. Variable oxidation states: Transition elements exhibit variable oxidation states because they can lose electrons from both 4s and 3d orbitals for bond formation e.g we have Fe²⁺ and Fe³⁺
3. Complex ion formation: Transition elements form complex ions due to the presence of vacant or empty d- orbitals in their ions.
4. Catalytic ability: The catalytic ability of transition metals is due to the fact that they exist in different oxidations states, hence they are used as catalyst. The partially filled d-orbital allows the exchange of electrons to and from molecules which enable them to act as catalyst.

EVALUATION:

1. State the blocks of the following elements: H, F, Na, Ca, Fe and Mn
2. State three properties of transition elements and explain any two of the properties.

 

 

 

PERIOD 4:  FAMILIES OF ELEMENTS.

Elements are arranged into groups or families and periods. Each group has been given a name to allow proper understanding during discussions on the periodic table.

Names of the different group (1-8) on the periodic table are shown below.

Group (i) i.e. Li, Na, K etc. ——– alkaline metals

Group (ii) i.e. Be, Mg, Ca, etc. —— Alkaline earth metals

Group (iii) i.e. B, Al, Ga, etc. ——- Boron family

Group (iv) i.e. C, Si, Ge, etc. ——— Carbon family

Group (v) i.e. N, P, As, etc. ———- Nitrogen family

Group (vi) i.e. O, S, Se, etc. ——— Oxygen family or Chalcogens

Group (vii) i.e. Fl, Cl, Br, etc. —— Halogens

Group (viii) or group O i.e. He, Ne, Ar, etc. —— Rare, inert, noble gases.

Transition Elements: These are between groups 2 and 3 on periods 4 and 5.

Lanthanides (Rare- earth elements): these are fifteen elements La- Lu.

Actinides: These are found on the seventh period AC –Lr.

Artificial Elements: These are elements with atomic numbers 93 to 103. They are products formed during chemical reactions. They are unstable and disintegrate in a short time e.g. Plutonium (Pu) and curium (Cm)

EVALUATION:

1. Four elements P, Q, R and S, have 1, 2, 3 and 7 electrons in their outermost shell respectively. What is the element that is unlikely to be a metal?
2. The elements listed below belong to the same group in the periodic table; ₉F, ₁₇Cl, ₃₅Br, ₅₃I

• What is the electronic structure of the first-member?
• What is the family name of the elements?
• Which of the elements has the strongest oxidizing ability?

GENERAL EVALUATION

OBJECTIVE TEST;

1. The period table is an arrangement of elements in order of their. (a) Relative molecular mass (b) mass numbers (c) molecular masses (d) atomic numbers.
2. Four elements T, X, Y, Z have 1, 2, 3 and 6 electrons in their outmost shells respectively. The element that is likely to be a non-metal is. (a) X (b)T (c) Z (d) Y
3. An atom with the electronic configuration: Is², 2s², 2p⁶, 3S², 3d¹, 4s² is that of:

(a) an alkali metal (b) an alkali earth metal (c) a transition metal (d) a halogen

4. An element whose atomic number is 19 is

(a) a noble gas (b) an alkali earth metal (c) An alkali metal (d) a transition metal

5. Group 0 or 8 elements are called. (a) Active elements (b) lanthanides (c) noble gas (d) alkali earth metals.

ESSAY QUESTIONS

1. A shortened form of the periodic table is shown below. Use it to answer questions a and b.

I          II                               III         IV         V          VI         VII        O

1.            A

 

2. B

C

3.

4. D E

 

• Which of the elements represented as A to E in the table above is
• A transition metal; (ii) an alkaline earth metal

(iii) The least reactive (iv) the most electronegative

2. State the four properties of transition elements (d-block)
3. Name one element in each case which

(a) forms an amphoteric oxide;

(b) Liberates hydrogen from cold water;

(c) Exists as a liquid at room

4. Give the names of the members of the alkaline earth metal family.

 

 

 

 

 

PERIOD 1AND 2: PERIODIC PROPERTIES. Some properties of the atom change along a group or across a period on the periodic table. Atomic radius which is measured of the size is one of such properties. The orbiting electrons in an atom are best represented by an electron cloud which has no distinct limit as the size of an action cannot be defined easily.

1. Atomic radius: This has been defined as the distance of closest approach to another identical atom in a given bonding situation. There are two types of atomic radii. Covalent radius and Van der Waals radius. Covalent radius is half the distance between two identical atoms which are not chemically bonded. For the two types of atomic radius two variations are noticeable:

• The atom radius increases down a group
• The atomic radius decreases along a period.

This is because going down any group on the periodic table the number of valence electrons remains constant while the shells increase in size (radius) despite increase in nuclear charge. The atomic radius of potassium is greater than that of Sodium. The atomic radius of caesium is greater than that of rubidium.

Across a period, electrons are added to orbitals in the same shell, all the valence electrons are therefore at the same energy level. As atomic number increase the positive charge of the nucleus increases giving rise to greater attraction between the positive nucleus and negative electrons. This is turn result in contraction of the electrons cloud resulting in a smaller atom. Atomic radii therefore decrease across a given period on the periodic table.

2. Ionic Radius: Ions are formed by a loss or gain of electrons by an atom. A positive ion (cation) is smaller than the original metal atom because electrons are pulled in due to increase in effective nuclear charge.

A negative ion (anion) is bigger than the corresponding non- metal atom because the effective nuclear charge is reduced.

As we move across the second short period, the cationicradii decrease from sodium to aluminium while the anionicradii increase from phosphorous to chlorine.

3. Ionization energy: Ionization occurs when gaseous atom loses electrons from its outer most shell to become positively charged

K

The energy required to do this is called ionization energy or ionization potential.

First ionization energy of an element is the energy needed to remove one mole of electron(s) from one mole of atoms in the gaseous state. It is expressed in kilo- joules per mole of atoms ionized.

First ionization energy increase across the period with noble gases having the highest. As we go down he the group, the value of first ionization energy decreases.

FIRST IONIZATION ENERGIES OF ALKALI METALS

 

Element	LI	Na	K	Rb	Cs
First ionization energy KJMOL-1	520	500	420	400	380

 

FIRST IONIZATION ENERGIES OF THE ELEMENTS IN THE THIRD PERIOD OF THE PERIODIC TABLE

Element	Na	Mg	Al	Si	P	S	Cl	Ar
First ionization energy KJMOL-1	496	737	577	786	1012	999	1255	1521

 

Three factors that affect the ionization potential of an atom

Ionization potential of an atom is affected by.

• Distance of the outer most electrons from the nucleus.
• Size of the positive or effective nuclear change.
• Screening effect of the inner electrons.

Moving from left to right across a period, there is a general rise in the first ionization energy. This is due to the fact that the nuclear charge is increasing across the period. This in turn causes a decrease in atomic radius that is a decrease in the distance of the outermost electrons from the nucleus. The screening effect is almost the same across the period.  Down a group of the periodic table, ionization energy decreases because the nuclear charge on the outermost electron is reduced. The outermost electron are properly shielded from the effect of nuclear charge

4. Electron Affinity: is the energy released when an electron is added to gaseous atom in its lowest energy state. Its unit is kJmol^-1 or electron volts (ev). Electron affinity increase across a period from left to right and decrease down the group on the periodic table.

Group 1 elements, alkali metals have the least tendency to add electrons to their neutral atoms.

Elements in groups VI and VII have greatest tendency to accept electron. Noble gases (group 8 or 0) have stable electronic configuration

5. Electronegativity: Electronegativity is the ability or power of that atom in a molecule to attract shared pair of electrons. It is more pronounced in heteronuclear molecules where two dissimilar atoms share one or more pairs of electrons.

Electronegativity increases across the period, i.e. going from left to right of the Periodic Table but decreases down the group i.e. going down the Periodic Table. The steady increase as one goes across the period is due to a steady increase in nuclear charge and decrease in atomic size. Consequently, the halogen atom, Fluorine, has the highest electronegativity in the period, due to the strong affinity for electrons.But down the group, the increase in atomic size due to screening effect of the inner shells of electrons decreases the nuclear attraction for shared electrons. The noble gases of group O are not assigned electronegativity values since they have completed shells of electrons.

EVALUATION

1. List three periodic properties of elements that generally increase the across the period of the Periodic Table.
2. Explain the term electron affinity and discuss how it varies across the period and down the group of the Periodic Table.

PERIOD 3: PERIODIC GRADATION OF THE ELEMENTS IN THE THIRD PERIOD (Na-Ar)

Gradation in properties is not confined only to the elements, but it is also found in their compounds with increasing atomic number.

The extent of hydrolysis of the chlorides changes across the third period. Sodium chloride is not hydrolyzed at all in aqueous solution. The same applies to magnesium chloride although hydrated crystals undergo hydrolysis when heated given off HCl and leaving a basic salt. An aqueous solution of aluminium chloride shows appreciable hydrolysis and turns blue litmus red. The chlorides of silicon, phosphorus and Sulphur hydrolyze completely in water.

The general conclusion from the above is therefore as follows: From left hand side to right hand side across any period of representative elements, the metallic character, i.e. tendency to lose electron(s)decreases, and the non-metallic character, i.e. tendency to gain electron(s)increases. Also, as one goes across the period, ionic property decreases while covalent property increases.

 

PERIOD 4: DIAGONAL RELATIONSHIP

Because metallic character increases down a groupand decreases from left to right along a period, there exists a diagonal relationship between the chemical properties of the first member of a group and that of the second member of the next group as in the cases of lithium and magnesium on one hand, and beryllium and aluminium on the other (see the periodic table)

 

EVALUATION

1. The atoms of four elements are represented as ₂₀Q, ₁₆R, ₁₀S and ₈ Which of the elements would be unreactive?
2. Explain the meaning of the diagonal relationship the periods 2 and 3 of elements in the Periodic Table.

GENERAL EVALUATION

OBJECTIVE TEST:

1. An element which has atomic number 11, is likely to have similar chemical properties with another element having atomic number. (a) 7 (b) 9 (c) 18 (d) 19
2. If the electronic configuration of an element X is 1s², 2S², 2P⁵, which of the following statements about X is false? It(a) Have five electrons in its valence shell. (b) Has atomic number 9(c) Is a halogen (d) Is a non-metal
3. The electronic configuration of an element X is 1s², 2s², 2p⁶ , 3s²,3P⁴. It can be deduced that X (a) Belongs to group 6 of the periodic table.(b) Belongs to period IV of the periodic table.(c) Has 3 unpaid electrons in its atom. (d) belongs to group 4
4. Which of the properties of the atom increases across the period and down the group in the periodic table? (a) Atomic radius (b) electronegativity (c) electropositivity (d) Ionic radius
5. Which of the following group 1 elements has the highest Ionization energy? (a) LI (b) Na (c) K (d) Rb

 

ESSAY QUESTIONS

1. (a) What are isoelectronic ions? (b) Give two examples, one each of a cation and an anion, which are isoelectronic with neon.
2. (a) Which of the following elements: calcium fluorine, iodine, neon, magnesium and helium are: (a) Halogens (b) noble gas (c) alkaline earth metal
3. List three periodic properties of elements that generally increase across the periodic table.
4. Arrange the following elements in order of decreasing electro negativity.

₁₆S, ₁₃Al, ₁₁Na, ₁₅P

5. State the periodic law.