Question

Complete each of the statements a through d using 1,2, or \(3:\) 1\. decreases 2\. increases 3\. remains the same Going from left to right across Period 4 , a. the ionization energy b. the atomic size c. the metallic character d. the number of valence electrons

Short answer

a. 2, b. 1, c. 1, d. 2

Step-by-step solution

Understanding Ionization Energy

Ionization energy is the energy required to remove an electron from an atom. As you move from left to right across Period 4, the ionization energy generally increases due to the increasing nuclear charge.

Understanding Atomic Size

Atomic size, or atomic radius, typically decreases as you move from left to right across a period. This is due to the increasing positive charge in the nucleus which pulls the electrons closer.

Understanding Metallic Character

Metallic character decreases as you move from left to right across a period. This is because atoms more easily lose electrons (more metallic) on the left, while atoms on the right tend to gain electrons (less metallic).

Understanding Number of Valence Electrons

The number of valence electrons increases as you move from left to right across Period 4. Elements gain more electrons in their outermost shell as you progress across the period.

Key concepts

Ionization Energy

Ionization energy is a measure of the energy needed to remove an electron from an atom. If we look at Period 4 of the periodic table, we see that ionization energy generally increases as we move from left to right. This happens because the nuclear charge (the number of protons in the nucleus) increases. A higher nuclear charge means that there is a stronger attraction between the nucleus and the electrons. Therefore, more energy is required to remove an electron.

Remember, ionization energy is crucial in determining how easily an element forms ions. High ionization energies usually mean that the element is less likely to lose an electron and form a positive ion (cation).

Atomic Size

Atomic size, also known as atomic radius, refers to the distance from the nucleus of an atom to its outermost electron. In Period 4, atomic size decreases from left to right. This trend is due to the increasing nuclear charge as you move across the period.

Even though more electrons are added to the outer shells, the increasing positive charge in the nucleus pulls these electrons closer. This results in a smaller atomic radius. Therefore, elements on the right side of Period 4 are smaller in size compared to those on the left.
Understanding this trend is important, as atomic size influences many properties of the element, such as bonding and reactivity.

Metallic Character

Metallic character describes the ability of an element to lose electrons and form positive ions. As you move from left to right across Period 4, metallic character decreases. This is because elements on the left side are more likely to lose electrons easily, making them more metallic.

On the right side of the period, elements are more likely to gain electrons and form negative ions (anions), making them less metallic. Metals are usually shiny, good conductors of electricity and heat, and malleable. Nonmetals, on the other hand, are not as shiny, poorer conductors, and brittle.
So, understanding where an element lies in Period 4 can give you a good indication of its metallic properties.

Valence Electrons

Valence electrons are the electrons in the outermost shell of an atom that are involved in chemical reactions and bonding. In Period 4, the number of valence electrons increases as you move from left to right across the period.

For example, potassium (K) has one valence electron, while krypton (Kr), at the end of the period, has eight valence electrons. Understanding this trend is important because the number of valence electrons determines an element's reactivity and the types of bonds it can form.
Elements with similar numbers of valence electrons often have similar chemical properties. Knowing the number of valence electrons can help predict how an element will interact with other elements.