6.3 Periodic Trends

Elements on the right side of the periodic table gain electrons to gain a stable octet.

An element forms a negative ion when ionized. On what side of the periodic table is the element located? Explain.

The n2²np⁶ electron configuration, known as the octet configuration, contains eight electrons and generally has the lowest energy and is the most stable. Atoms gain, lose, or share electrons in order to obtain the stable octet configuration. Hydrogen and helium have a complete energy level with just two valence electrons.

Explain the octet rule. Why are hydrogen and helium exceptions to the octet rule?

Atomic radii decrease left-to-right because the nuclear charge increases as the shielding of inner core electrons remains constant. The increased attraction of the nucleus for its electrons pulls the electrons inward, resulting in a decreased atomic size.

Explain why atomic radii decrease as you move from left to right across a period.

With each removed electron, there are fewer electrons to shield the remaining electrons from the electrostatic force of attraction of the nucleus. The increased nuclear attraction makes it more difficult to remove subsequent electrons.

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

The ionic radius of a nonmetal is larger than its neutral atom. Nonmetals tend to gain electrons in the atom's current energy level; these additional electrons repel each other and increase the size of the ion.

How does the ionic radius of a nonmetal compare with its atomic radius? Explain the change in radius.

1; 8

How many valence electrons do elements in group 1 have? In group 18?

Ba²⁺ is the largest; Mg²⁺ is the smallest; ionic size increases down a group.

Of the elements magnesium, calcium, and barium, which forms the ion with the largest radius? The smallest? What periodic trend explains this?

When silicon and oxygen bond, silicon atoms become smaller as they lose electrons, and oxygen atoms become larger as they gain electrons.

Soft contact lenses are made of silicon and oxygen atoms bonded together. Create a table listing the atomic and ionic electron configurations, and the atomic and ionic radii for silicon and oxygen. When silicon bonds with oxygen, which atoms become larger and which become smaller? why?

Carbon atoms decrease in size. Nitrogen and oxygen atoms increase in size.

Some diet sodas contain the artificial sweetener aspartame, a compound containing carbon, nitrogen, oxygen, and other atoms. Create a table showing the atomic and ionic radii of carbon, nitrogen and oxygen. (Assume the ionization states shown in Figure 6.14 of your textbook). Use the table to predict whether the sizes of carbon, nitrogen, and oxygen atoms increase or decrease in size when they form bonds in aspartame.

a) chlorine, carbon, oxygen b) chlorine, oxygen, carbon

Some sports bottles are made of Lexan, a plastic containing a compound of the elements chlorine, carbon, and oxygen. Order these elements from greatest to least according to atomic radius and ionic radius.

No, the electron configuration of a chlorine ion and an argon atom are the same, but the chlorine ion still has 17 protons and retains its identity as chlorine.

The electron configuration of a chlorine atom is [Ne]3s²3p⁵. When it gains an electron and becomes an ion, its electron configuration changes to [Ne]3s²3p⁶, or the electron configuration for argon. Has the chlorine atom changed to an argon atom? Explain.

a) the ion is negative. a negative ion is always larger than its atom b) A is the the left of B. Atomic radius in a period decreases left-to-right. c) A is below B. Ionic radius increases down a group

Use Figure 6.20 to answer each of the following questions. Explain your reasoning for each answer. a) if A is an ion and B is an atom of the same element, is the ion a positive or negative ion? b) If A and B represent the atomic radii of two elements in the same period, what is their order? c) If A and B represent the ionic radii of two elements in the same group, what is their order?

Ionization energy is the energy needed to remove an electron from a neutral atom in its gaseous state.

What is ionization energy?

a) N b) Ne c) Li

Which element has the larger ionization energy? a) Li or N b) Kr or Ne c) Cs or Li