Question

1. the effective nuclear charge, ( z_{eff}), experienced by valence electrons in an atom can be estimated from the equation ( z_{eff})= the number of protons - the number of core electrons. using this estimation, the effective nuclear charge for main - group elements would ______________ from left to right across a period.

a. increases
b. decreases
c. stays the same
d. goes up and down

1. a main - group element has 81 protons and an estimated effective nuclear charge of 3+. therefore the element has __________ core electrons and can be found in group ____ on the pt.

a. 84 core electrons a. group 3a
b. 78 core electrons b. group 3b
c. 82 core electrons c. group 5a
d. 27 core electrons d. group 6a

1. the diagram shows the electron structures of two alkali metals and two halogens. when these elements react and form compounds, alkali metals lose their one valence electron while halogens gain one additional electron to their valence shell. the vigor of the reaction is directly related to the distance of the valence electrons from the attractive pull of the atoms nucleus. for alkali metals, it becomes easier to lose the valence electron with increasing distance of that electron from the attractive pull of the nucleus. for halogens, it becomes easier to gain an additional electron to their valence shell with decreasing distance of that shell to the attractive pull of the atoms nucleus.

for the given elements, which reaction will proceed most quickly or be the easiest?
a. li and f
b. li and cl
c. na and f
d. na and cl

1. a mystery element has 18 protons. which one of the following statements is true?

a. the element belongs in row 2 of the periodic table and is classified as a halogen.
b. the element belongs in row 3 of the periodic table and is classified as a noble gas.
c. the element belongs in row 4 of the periodic table and is classified as an alkali metal.
d. the element belongs in row 5 of the periodic table and is classified as an alkaline - earth metal.

Explanation:

Step1: Analyze question 7

As we move from left - to - right across a period, the number of protons increases while the number of core electrons remains the same. Using the formula $Z_{eff}=\text{number of protons}-\text{number of core electrons}$, the effective nuclear charge increases.

Step2: Analyze question 8

Given $Z_{eff}=\text{number of protons}-\text{number of core electrons}$. If number of protons = 81 and $Z_{eff}=3+$, then number of core electrons = 81 - 3=78. Main - group elements with 3 valence electrons are in group 3A.

Step3: Analyze question 9

Sodium is more reactive than lithium as the valence electron in sodium is further from the nucleus and easier to lose. Fluorine is more reactive than chlorine as its valence shell is closer to the nucleus and it is easier for it to gain an electron. So the reaction between Na and F will be the most vigorous.

Step4: Analyze question 10

An element with 18 protons is argon (Ar). Argon has an electron - configuration of 2, 8, 8 and is in row 3 of the periodic table and is a noble gas.

Answer:

1. A. Increases
2. No correct core - electron option given; A. group 3A
3. C. Na and F
4. B. The element belongs in row 3 of the periodic table and is classified as a noble gas (assuming the full option was about it being a noble gas)