Question 1

What are valence electrons and why do they matter in chemistry?

Accepted Answer

Valence electrons are the outermost electrons in an atom, held most loosely and farthest from the nucleus. They play the most important role in chemical bonding because they are the easiest to lose or share. Elements with the same number of valence electrons exhibit similar chemical properties, which is why the periodic table groups them together.

Question 2

How does the periodic table organize elements by their electron configurations?

Accepted Answer

The periodic table arranges elements by increasing atomic number so that elements with similar outer electron configurations recur periodically. For main-group elements, the group number equals the number of valence electrons, and the row number equals the highest principal quantum number. This organization reflects the periodic recurrence of similar electron configurations in outer shells.

Question 3

What distinguishes alkali metals from other main-group elements?

Accepted Answer

Alkali metals are Group 1 elements (except hydrogen) with only one valence electron in their outermost s-orbital. Because they have just one electron available for bonding, they are extremely reactive. Their single valence electron makes them eager to lose it and form positive ions in chemical reactions.

Question 4

Why are noble gases so unreactive?

Accepted Answer

Noble gases have eight valence electrons in their outermost shell, except helium which has two. This complete valence shell makes them highly stable and unreactive because they have no tendency to gain, lose, or share electrons. Their filled outer electron configuration means they do not participate readily in chemical bonding.

Question 5

What are transition metals and how do they differ from main-group elements?

Accepted Answer

Transition metals are d-block elements where the last electron enters a d-orbital. Unlike main-group elements, their valence electrons include both the outermost s electrons and the (n-1) d electrons. The d-block contains ten columns because five d-orbitals can hold a maximum of ten electrons total.

Question 6

How are inner transition elements organized in the periodic table?

Accepted Answer

Inner transition elements form the f-block, where the last electron enters an f-orbital. They are arranged in two series: the lanthanide series and the actinide series. The principal quantum number of the f-orbitals that fill is two less than the row number, and the f-block contains fourteen columns representing seven f-orbitals.

Question 7

How does the number of valence electrons change across a period and down a group?

Accepted Answer

Across a period, the number of valence electrons increases by one with each consecutive element. Down a group, the number of valence electrons remains the same while the principal quantum number increases by one. This pattern explains why elements in the same group share similar chemical properties despite being in different periods.

元素の周期的分類

Browse More Videos