Periodicity & The Periodic Table

How are elements in the Periodic Table arranged?

Elements are arranged in order of increasing atomic number.

What is a row in the Periodic Table known as?

A row in the Periodic Table is known as a period.

Why are elements placed in the same group?

Elements are placed in the same group because they have the same number of electrons in the outer shell.

Why are sodium and magnesium both in Period 3 of the Periodic Table?

Sodium and magnesium are in Period 3 because they both have their outer electron in the 3rd energy level.

True or False: Group 17 elements react in a similar way because they have the same number of electron shells.

False.

Why do Group 7 elements react in a similar way?

Group 7 elements react in a similar way because they have the same number of electrons in their outermost shell.

What are outer electrons also known as?

Outer electrons are also known as valence electrons.

What are the four main blocks in the Periodic Table?

The four main blocks are s-block, p-block, d-block, and f-block.

Why is sodium located in the s-block of the Periodic Table?

Sodium is in the s-block because its outer electron is in the s subshell.

Which block does the element with the electronic configuration 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p4 belong to?

This element is in the p-block.

In which period and group is the element with the electronic configuration 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p4 located?

It is in Period 4, Group 6.

Why is hydrogen placed in a group on its own?

Hydrogen is placed in a group on its own because it does not share physical and chemical properties with members of the other groups.

What information does the electron configuration provide about an element's position in the Periodic Table?

It provides information about an element's period, group, and block.

What is Group 1 of the Periodic Table called?

Group 1 is called the alkali metals.

Which group of the Periodic Table are the halogens?

The halogens are Group 17.

What is Group 18 of the Periodic Table called?

Group 18 is called the noble gases.

Where are transition elements located in the Periodic Table?

Transition metals are located in the d-block.

True or False: The period number shows the outer energy levels occupied by electrons.

True.

What is the electronic configuration of an element located in Group 2, Period 3?

The electronic configuration is 1s2 2s2 2p6 3s2.

What is the electronic configuration of an element located in Group 17, Period 4?

The electronic configuration is 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p5.

Where is the element with the electronic configuration [Ar] 3d6 4s2 located in the Periodic Table?

This element is a transition element, located in the d-block of Period 4.

True or False: The number of valence electrons always equals the group number for all elements.

False.

When does the number of valence electrons equal the group number?

It equals the group number for main group elements, but not for transition elements.

Define ionisation energy.

Ionisation energy is the amount of energy required to remove one mole of electrons from one mole of atoms in the gaseous state.

Explain the trend in atomic radius across Period 3.

Atomic radius decreases because the nuclear charge increases, leading to a greater attraction between the nucleus and electrons.

Define electron affinity.

Electron affinity is the amount of energy released when one mole of electrons is gained by one mole of atoms in the gaseous state.

Explain the trend in electronegativity down a group.

Electronegativity decreases because nuclear charge, atomic radius, and shielding by inner electrons increase.

What happens to electronegativity as you go down a group?

Electronegativity decreases because the nuclear charge, atomic radius, and shielding by inner electrons increase, leading to less attraction between the nucleus and outer bonding electrons.

True or False: Atomic radii increases going down a group.

True.

Why does the first ionisation energy increase across a period?

The first ionisation energy increases across a period because the nuclear charge increases while shielding remains similar, and the distance between the nucleus and outer electron stays reasonably constant, requiring more energy to remove an electron.

What is the unit of electron affinity?

kJ mol-1.

True or False: Electron affinities generally increase down a group.

False. Electron affinities generally decrease down a group.

What trend occurs in electronegativity as you go across a period?

Electronegativity increases.

Why is the ionic radius of Mg2+ smaller than that of Na+?

The ionic radius of Mg2+ is smaller because the magnesium ion has a higher nuclear charge and fewer electrons, resulting in a greater force of attraction between them.

What are the two products formed when sodium reacts with water?

Sodium hydroxide and hydrogen.

Name two properties of Group 1 metals.

1. They are soft. 2. They have relatively low densities. 3. They have relatively low melting points. 4. They are very reactive.

Why do alkali metals share similar chemical properties?

They share similar chemical properties because they have the same number of electrons in their outer shell.

What is the word equation for the reaction between lithium and water?

Lithium + water → lithium hydroxide + hydrogen.

What is the balanced symbol equation for the reaction between potassium and water?

2K (s) + 2H2O (l) → 2KOH (aq) + H2 (g).

What product is formed when sodium reacts with oxygen?

Sodium oxide.

Describe the trend in reactivity going down Group 1.

Reactivity increases.

Apart from fizzing, what are two other observations when sodium is added to water?

1. Floating. 2. Melting into a ball.

Describe the trend in melting point going down Group 1.

Melting point decreases.

True or False: The density of Group 1 elements increases going down the group.

True.

Why are Group 1 metals known as alkali metals?

They are known as alkali metals because they form alkaline solutions when added to water.

Why does the reactivity of Group 1 metals increase down the group?

Reactivity increases because the outer electron is further from the nucleus and more shielded, resulting in a weaker force of attraction, making it easier to lose the outer electron.

True or False: All alkali metals react vigorously with halogens to form alkali metal halide salts.

True.

How do halogens form halide ions?

Halogens form halide ions by gaining one electron to complete their outer shell.

True or False: The reactivity of halogens increases as you go down Group 17.

False. The reactivity of halogens decreases as you go down Group 17.

What is a halogen displacement reaction?

A halogen displacement reaction occurs when a more reactive halogen displaces a less reactive halogen from an aqueous solution of its halide.

What is the trend in melting and boiling points of halogens down Group 17?

Melting and boiling points increase as you go down Group 17.

Can chlorine displace iodine from an aqueous solution of potassium iodide?

True.

Why does the reactivity of halogens decrease down Group 17?

Reactivity decreases due to increased electron shielding and distance from the nucleus, making it harder to gain an electron.

What is the color and state of chlorine at room temperature?

Chlorine is a pale yellow-green gas.

What is the color and state of iodine at room temperature?

Iodine is a grey-black solid.

Are the halogens monoatomic or diatomic?

False, the halogens are diatomic.

What is the balanced symbol equation for the reaction between potassium iodide and bromine?

Br2 + 2KI → 2KBr + I2.

Why can't iodine displace chlorine from potassium chloride?

Iodine cannot displace chlorine because it is less reactive.

What color will the solution turn when chlorine displaces bromine from potassium bromide?

The solution will turn orange.

What happens when potassium iodide reacts with bromine?

A brown solution is formed.

What is the general trend in the acid-base character of oxides across a period?

The character changes from basic to amphoteric to acidic.

What is an oxide that can act both as a base and an acid called?

An amphoteric oxide.

What is the amphoteric oxide in Period 3?

Aluminium oxide.

Do metallic oxides generally form acids or bases when they react with water?

False, they form hydroxides (bases).

What type of compounds do non-metallic oxides form when they react with water?

Non-metallic oxides form acids.

What is the balanced symbol equation for the reaction between magnesium oxide and water?

MgO (s) + H2O (l) → Mg(OH)2 (aq).

What is the pH of the solution formed when NO2 is added to water?

The pH is 1.

How does the pH of solutions formed by metal oxides change across a period?

The pH decreases (becomes less basic) across a period.

Do the oxides of elements become more or less ionic as you go across a period?

False, they become less ionic and more covalent.

What product is formed when SO2 is added to water?

Sulfurous acid, H2SO3 (aq).

Does calcium oxide form a solution with a higher or lower pH than sodium oxide when added to water?

False, calcium oxide forms a solution with a lower pH.

What type of structure does SiO2 have?

SiO2 has a giant covalent structure.

What are the two products formed when NO2 is added to water?

HNO3 and HNO2.

What is the definition of oxidation state?

It is a number assigned to an atom to show the number of electrons transferred in forming a bond.

Are oxidation states always positive?

False, oxidation states can be positive, negative, or zero.

What is the oxidation number of an atom in its elemental state?

The oxidation number is 0.

What is the oxidation number of hydrogen in most compounds?

The oxidation number of hydrogen is +1.

What is the oxidation number of oxygen in most compounds?

The oxidation number of oxygen is typically -2.

What is the oxidation number of oxygen in most compounds?

The oxidation number of oxygen in most compounds is -2.

What is the oxidation state of Group 2 elements?

The oxidation state of Group 2 elements is +2.

What is the oxidation number of sulfur in SO42-?

The oxidation number of sulfur in SO42- is +6.

What is the oxidation state of oxygen in hydrogen peroxide, H2O2?

The oxidation state of oxygen in hydrogen peroxide, H2O2, is -1.

True or False: In either a compound or an ion, the more electronegative element is given the positive oxidation number.

False.

What is the oxidation state of an element in mono-atomic ions?

The oxidation state of an element in mono-atomic ions is always the same as the charge.

What is the oxidation state of hydrogen in sodium hydride, NaH?

The oxidation state of hydrogen in sodium hydride, NaH, is -1.

What is the oxidation state of Zn?

The oxidation state of Zn is 0 because it is an element.

True or False: The oxidation state of Fe2+ is +2.

True.

What is the oxidation state of aluminium in Al2Cl6?

The oxidation state of aluminium in Al2Cl6 is +3.

What is the oxidation state of Mn in KMnO4?

The oxidation state of Mn in KMnO4 is +7.

What is the trend in ionization energy between periods?

There is a rapid decrease in ionization energy between the last element in one period and the first element in the next period.

What causes the decrease in ionization energy between beryllium and boron?

The decrease is caused by the fifth electron in boron entering the 2p subshell, which is further from the nucleus than the 2s subshell of beryllium.

What causes the decrease in ionization energy between nitrogen and oxygen?

The decrease is due to spin-pair repulsion in the 2p subshell of oxygen.

What is spin-pair repulsion?

Spin-pair repulsion is the repulsion between electrons of opposite spin in the same orbital.

Describe the general trend in ionization energy across a period.

Across a period, the ionization energy generally increases.

True or False: The discontinuity in the trend of ionization energy across a period provides evidence for energy sublevels.

True.

Explain why there is a decrease in first ionization energy between the last element in one period and the first element in the next period.

The decrease is due to increased distance between the nucleus and outer electron and more shielding by inner electrons.

True or False: The first ionization energy of sodium is higher than that of neon.

False.

What are two characteristic properties of transition elements?

Variable oxidation states and high melting points.

What causes the variable oxidation states in transition elements?

The presence of electrons in both 4s and 3d orbitals that can be lost.

True or False: All transition elements have strong magnetic properties.

False.