Periodic trends

​Objectives

• ​To list and interpret the factors that affect the trends in atomic radius, ionic radius, ionization energy, electron affinity and electronegativity of elements

• To compare atomic radius, ionic radius, ionization energy, electron affinity and electronegativity of elements

• To comapre the size of atoms to their ions

• To compare successive energies and to determine valence electrons

Subject | Subject

Warm-up: Drop quiz​

Subject | Subject

Periodic trends

• ​The five periodic trends are:

  1. Atomic radius

  2. Ionic radius

  3. Ionization energy

  4. Electronegativity

  5. Electron affinity

Subject | Subject

Hands-on activity​ using magnets

Subject | Subject

Factors that affect the periodic trends

• The force of attraction between valence electrons and nucleus

• The force strength depends on two factors:

  1- Shielding( distance)

  2- Effective nuclear charge

• As distance increases, the force decreases

• As the number of protons increases, the effective nuclear charge increases, and thus the force becomes stronger

• Across a period: ENC increases across a period from left to right due to increasing nuclear charge with no accompanying increase in the shielding effect.

  Down a group: ENC decreases down a group; although nuclear charge increases down a group, shielding effect more than counters its effect.

Atomic radius

• It reflects the size of the elements

• By definition, it is half the distance between two bonded nuclei

Classroom Resources | Periodic Trends: Ionization Energy, Atomic Radius & Ionic Radius | AACTiconiconiconiconicon

You can open this webpage in a new tab.

Copy link

Open in new tab

Atomic radius

• Increases down the group( from top to bottom) because of increased shielding

• Increases from right ​to left of the periodic table because of less effective nuclear charge

Across a period: Radius decreases

Down a group: Atomic radius increases​

​

​Atomic radius

Multiple Choice

As you move down a Group on the periodic table, what happens to the size of the atoms?

• they stay the same

• they get larger

• they get smaller

Multiple Choice

Which atom has the largest atomic radius?

• potassium
• rubidium 
• francium
• cesium

Multiple Choice

List these 3 elements in order of increasing atomic radius:

Be, F, C

• Be, F, C

• Be, C, F

• F, C, Be

• Same trend as atomic radius

• Across a period: Radius decreases

• ​Down a group: Ionic radius increases​

​

Ionic radius

Reason(Explain) for change in size

• ​Across a period: More protons, a higher effective nuclear charge means stronger attraction, less size, and vice versa.

• ​​Along a group: More energy levels added, more shielding and thus weaker force of attraction and larger size.

Periodic Trends Concept Builder

You can open this webpage in a new tab.

Copy link

Open in new tab

Ionization energy

• ​The energy required to remove an electron from a gaseous atom

• First ionization energy :X(g) + IE → X1+(g) + e–

  It is the amount of energy needed to remove an electron from a gaseous atom to form a single positively charged gaseous ion.

• Atoms with large ionization energy values are less likely to form positive ions. Low ionization energy indicates an atom loses an outer electron easily.​

Classroom Resources | Periodic Trends: Ionization Energy, Atomic Radius & Ionic Radius | AACTiconiconiconiconicon

You can open this webpage in a new tab.

Copy link

Open in new tab

Ionization energy

• ​The energy required to remove an electron from a gaseous atom

• Decreased down the group( from top to bottom) because of increased shielding

• Increases from left to right of the periodic table because of less effective nuclear charge

Ionization energy- Explanation

• ​Across a period: More protons, a higher effective nuclear charge means stronger attraction, more ionization energy, and vice versa.

• ​​Along a group: More energy levels added, more shielding and thus weaker force of attraction and less ionization energy.

Multiple Choice

Ionization energy is...

• the energy required to add an electron to a specific atom
• how much energy it takes to remove an electron from an atom
• the energy required to shield the outer electrons from the nucleus
• a measure of the ability of an atom to attract electrons

Multiple Choice

Which element has the greatest ionization energy: Aluminum (Al)    or    Chlorine (Cl)?

• Aluminum (Al)
• Chlorine (Cl)

Multiple Choice

Which of the following will have a lower ionization energy than Scandium (Sc)?

• Helium (He)
• Titanium (Ti)
• Calcium (Ca)
• Magnesium (Mg)

Ionization energy trend

​Exceptions in Ionization energy

​Groups 2 and 3

IE1 of group 2 elements involves the removal of an ns electron while that of group 3 involves the removal of a np electron. p-electron is more energetic than s-electron and easier to remove, thus IE1 of group 2 elements is greater than IE1 of group 3 elements.

​Exceptions in Ionization energy

​Groups 5 and 6 IE1 of group 5 involves the removal of np3 electron while that of group 6 involves the removal of np4. np4 has higher electron-electron repulsion hence less energy is needed to remove the electron, thus IE1 of group 5 elements is greater than IE1 of group 6 elements

• Energy required for each successive ionization energy always increases.

  The second ionization energy involves the removal of an electron from a positively charged ion where the attraction of the electron to the nucleus is higher, thus more energy is needed.

​

Ionization energy

​

​Huge jumps are use to determine the number of valence electrons

Importance of sucessive IE

Successive ionization energies

​Explain why each successive ionization of an electron requires a greater amount of energy

​Each successive electron removed from an ion feels an increasingly stronger effective nuclear charge, thus more energy is needed to remove an electron.

Multiple Choice

Put the following in order of increasing ionization energy:Neon, Lithium, Carbon

• Lithium, Carbon, Neon
• Carbon, Lithium, Neon
• Neon, Carbon, Lithium
• Lithium, Neon, Carbon

Multiple Choice

Which equation correctly describes the first ionization energy of X?

• X --> X^- + e^-

• X --> X⁺ + e^-

• X --> X^- + e⁺

• X + e^- --> X^-

• X + e^- --> X⁺

​Electronegativity

​Electronegativity is the relative ability of atoms to attract electrons in a chemical bond.

Electron affinity

Electron affinity is the amount of energy released when an electron is added to the atom in its gaseous state.

• ​Across a period from left to right, the electron affinity becomes more negative (increases) because the higher effective nuclear charge increases the nuclear attraction for the incoming electron

• ​Down a group, the electron affinity does not change very much because the lower-electron nucleus attraction down the group is evenly counterbalanced by a simultaneous lowering in the electron- electron repulsion

Summary

Multiple Choice

Which of the following is the least electronegative element?

• oxygen
• potassium
• fluorine
• nitrogen

Multiple Choice

Put these in order of increasing electronegativity:
Se, S, and O

• Se < S < O
• Se < O < S
• O < S < Se
• S < Se < O

Multiple Choice

As you move down the periodic table atoms get bigger.  This is because ____________.

• The atoms have more mass.
• The atoms have more protons.
• The atoms have more energy levels
• The atoms have more nuetrons

Multiple Choice

Which atom has the largest atomic radius?

• potassium
• rubidium 
• francium
• cesium

Multiple Choice

Which element has the greatest ionization energy: Aluminum (Al)    or    Chlorine (Cl)?

• Aluminum (Al)
• Chlorine (Cl)

Multiple Choice

Which element in Period 2 has the greatest atomic radius?

• Be

• C

• Na

• Li

Multiple Choice

which of the following families is the least electronegative?

• noble gases

• Halogens

• transition metals

• alkali metals

Multiple Choice

The picture shows what trend?

• Electronegativity
• Atomic Number
• Atomic Radius
• Ionization