Complete each of the statements a to d using 1, 2, or 3:
1. decreases
2. increases
3. remains the same
Going from left to right across Period 4,
d. the number of valence electrons ________

Verified step by step guidance

1. Understand the periodic table layout: Period 4 refers to the fourth row of the periodic table, which includes elements from potassium (K) to krypton (Kr).
2. Recall the concept of valence electrons: Valence electrons are the outermost electrons of an atom and determine its chemical properties. For main group elements, the number of valence electrons corresponds to the group number (1A to 8A).
3. Analyze the trend across a period: As you move from left to right across a period, the number of valence electrons increases by one for each successive element in the main group elements.
4. Apply this trend to Period 4: Starting with potassium (K) in Group 1A, which has 1 valence electron, and ending with krypton (Kr) in Group 8A, which has 8 valence electrons, the number of valence electrons increases across the period.
5. Conclude that the correct answer for part d is '2. increases,' as the number of valence electrons increases from left to right across Period 4.

Key Concepts

Periodic Trends

Periodic trends refer to the predictable patterns observed in the properties of elements as you move across a period or down a group in the periodic table. These trends include atomic radius, ionization energy, electronegativity, and the number of valence electrons, which help in understanding how elements behave chemically.

Valence Electrons

Valence electrons are the electrons located in the outermost shell of an atom and are crucial for determining an element's chemical properties and reactivity. The number of valence electrons influences how an element bonds with others, and in Period 4, elements typically have a consistent increase in valence electrons as you move from left to right.

Period 4 Elements

Period 4 of the periodic table includes elements from potassium (K) to krypton (Kr). As you progress across this period, the atomic number increases, leading to an increase in the number of protons and electrons, which directly affects the number of valence electrons, typically increasing from 1 to 8.