Chapter 3 Test: Periodic Trends

What is the trend across and down the periodic table for Atomic radius?

Across - atomic radius decreases Down - atomic radius increases

What is the trend across an down the periodic table for Electronegativity?

Across: EN increases Down: EN decreases

What is the trend across an down the periodic table for Ionization energy?

Across: IE increases Down: IE decreases

Define amphoteric and identify the periodic 3 oxide that is amphoteric.

Amphoteric means a substance can act as an acid and a base depending on the conditions. Al2O3 is amphoteric.

Give two reasons for increasing atomic radius down a group on the periodic table

Atomic radius increases going down a group because the electrons are added to energy levels that are farther from the nucleus and The outer electrons are shielded from the full attraction of the nucleus by the electrons in inner energy levels

Explain the trend in reactivity in group 7 in terms of electron affinity.

Electron affinity decreases going down a group because electrons are farther from the nucleus and are shielded by the inner electrons. Chlorine has a higher electron affinity than bromine which means that it would like electrons more than bromine. So, chlorine is likely to be more reactive than Br2 and I2. Chlorine is also a stronger oxidizing agent than bromine and bromine is a stronger oxidizing agent than iodine.

Which properties decrease down group 1 in the periodic table?

Electronegativity, electron affinity, ionization energy, melting point

Which properties decrease down group 7 in the periodic table?

Electronegativity, electron affinity, ionization energy, reactivity

List some observations you could make while observing lithium react with water.

Fizzing (formation of hydrogen gas) Heat and light (exothermic reaction) Formation of alkaline solution Metals seem to float on water and move around

Suggest a reason that melting point decreases down group 1 on the periodic table.

Group 1 elements are all metals and therefore bond via metallic bonding - positive nuclei in an electron sea. Because of increased shielding the nuclei have less attraction for the electrons. Also, because there are more electrons, there are increased repulsion between the atoms. Cesium can be melted by holding it in your hand.

Suggest a reason that melting point increases down group 7 on the periodic table.

Group 7 are all non-metals and therefore bond via atomic network bonding. The electrons are not delocalized as they are in metals so the bonding is not as strong as it is in metals. So this explains why fluorine and chlorine are gases at room temperature. As the number of electrons increase, there is increased dispersion forces which explain why bromine is a liquid and iodine is a solid. Dispersion forces are very weak, however, bromine is very volatile and iodine sublimes when open to the air.

Give two reasons for lower ionization energy going down a group on the periodic table.

Ionization energy decreases going down a group because the electrons are farther from the nucleus b/c they are added to outer energy levels. Furthermore the electrons are shielded from the full attraction of the nucleus by the electrons in inner energy levels

Explain why the first ionization energy of oxygen is slightly less than that of nitrogen.

Ionization energy generally increases across a period so oxygen should have a higher ionization energy than nitrogen but it doesn't. If you look at the orbital diagrams for nitrogen and oxygen you will see that oxygen has one p orbital with two electrons and two other p orbitals with one electron each. The added repulsion from the two electrons in one orbital and the fact that there is some stability gained by having a half-filled sub-level, explains why it is easier to take an electron from oxygen than nitrogen. Nitrogen already has a half-filled sub-level.

Write reactions for lithium and water and potassium and water.

Li + H2O to LiOH + H2 K + H2O to KOH + H2

Explain why the first ionization energy for boron is slightly less than that of magnesium.

Magnesium has two electron in the s sublevel while boron has two in the s sublevel and one in the p sublevel. Boron is more willing to give up its p than Mg is to give up one of its S electrons because there is some stability gained in having a filled sublevel.

List some observations you could make when halide ions are mixed with silver ions.

Most silver halide compounds are insoluble in water so a precipitate will form AgCl is white AgBr is cream/light yellow AgI is yellow AgF is soluble in water

Explain why Sodium Oxide forms a stronger base in water than Magnesium oxide.

Na2O separates into Na+ and O2-, O2- is a very strong base and takes a hydrogen from water. With Mg2+, the oxide is also strongly attracted to the more highly charged Mg2+ ion and therefore has less of an ability to steal protons from water.

List the oxides formed by the period three elements.

Na2O, MgO, Al2O3, SiO2, P4O10, SO3, Cl2O7

Br2 + Cl- to ?

No

I2 + Br- to ?

No

I2 + Cl- to ?

No

Explain the trend in reactivity in group 1 in terms of ionization energy.

Since ionization energy increases going down a group it is easier for K to lose an electron than for Lithium to lose an electron, therefore K will be more reactive than lithium. **More energy is given off, though, in the lithium -water reaction because lithium has a higher charge density so more energy is released when water molecules surround the lithium atom.

State whether the resulting solutions will be acidic, neutral or alkaline.

The solutions will be alkaline (basic) because of the presence of OH- ion.

Describe the trend in acid/base properties from left to right

The trend is strong base (Na2O) to weak base (MgO) to amphoteric (Al2O3) to weak acid (P4O10) to strong acid (SO3 + Cl2O7). These compounds become acidic/basic only when dissolved in water.

What two forces are responsible for the trends listed above?

The two forces are the attractive force of the nucleus and the repulsive force of the electrons

Explain why SiO2 is considered an acid even though it is insoluble in water.

Water can't break apart the strong Si-O bonds so it's insoluble but is classified as an acid because when it reacts with a base it forms a neutral salt. Remember that the products of neutralization reactions are water and a salt. So, if SiO2 reacts with a base and makes a neutral solution, it must be acidic.

Describe the change in atomic radius when anions form.

When anions form, electrons are gained. The nucleus cannot overcome the added repulsion of the electrons and the radius increases. The more negative, the larger the ion.

Describe the change in atomic radius when cations form.

When cations form, electrons are lost. With fewer electrons, there is less repulsion and the electrons are pulled closer to the nucleus. Therefore, for positive ions, radius decreases. The more positive, the smaller the ion.

Br2 + I- to ?

Yes Br- + I2

Cl2 + Br- to ?

Yes Cl- + Br2

Cl2 + I- to ?

Yes Cl- + I2

What increases in equal steps of one from left to right in the periodic table for the elements lithium to neon?

atomic #

Reactivity with water increases/decreases going down the periodic table for group I.

increases

Explain why the second ionization energy for magnesium is lower than that for sodium.

ionization energy generally increases across a period so this seems like an exception except that sodium only has one valence electron while magnesium has 2. Sodium only needs to lose one electron to have a stable noble gas configuration and once it loses it, it is very unwilling to give up a second electron. Magnesium, on the other hand, easily gives up its second electron since it needs to lose two to have the stable noble gas configuration. Second ionization energy refers to the energy it takes to remove an electron after one electron as already been removed.

Give two reasons for the increase in ionization energy going across a period from left to right.

ionization energy increases across a period because the electrons are closer to the nucleus and because there are more protons attracting the electrons. The electrons are closer to the nucleus because within a period, they are added to the same energy level at the same rate that protons are added to the nucleus which increases the attraction of the electrons to the nucleus and drawing them closer.

Give two reasons for the decrease in atomic radius going across a period from left to right.

the atomic radius decreases because nuclear charge increases and electrons within a period are added to the same energy level. The increased nuclear charge pulls electrons closer - decreasing the radius.