Question

ionization energy is the energy needed to remove a valence electron from an atom. ionization energy increases going from left to right across a period of the periodic table because the atomic radius decreases, which means that the valence electrons are held more tightly by the nucleus. ionization energy decreases going down a group because the valence electrons are farther away from and more loosely held by the nucleus.

1. metals react by losing electrons (oxidation). group 1 metals (called the alkali metals) are the most reactive metals, because they have only one valence electron to lose. activity of metals decreases going across each period to groups 2 and 13. groups 3 through 12 contain the transition elements. they are all metals, but less reactive than those in group 1 and 2. their oxidation states cannot be easily predicted, and so gives us their names. example: iron (iii) means fe³⁺; copper (ii) means cu²⁺
2. the non - metals gain electrons (reduction) when they react. group 17 non - metals (called the halogens) are the most reactive non - metals because they have only one electron to gain to get a stable valence shell with eight electrons. activity decreases in groups 16 and then 15.
3. elements in group 18 (called the noble gases) have all their principal energy levels filled with electrons and so have little chemical reactivity.

check your understanding

1. an atom with atomic number 48 and mass number 120 contains:

a. 48 protons, 48 electrons, 72 neutrons
b. 72 protons, 48 electrons, and 48 neutrons
c. 120 protons, 48 electrons, and 72 neutrons
d. 72 protons, 72 electrons, and 48 neutrons

1. an element which has a mass number of 23 and has 12 neutrons is the element:

a. lithium
b. potassium
c. magnesium
d. sodium

1. the nucleus of the atom has

a. a high density
b. a low density
c. a negative charge
d. no charge

1. an ion always contains

a. unequal number of protons and electrons
b. equal number of protons and electrons
c. unequal number of protons and neutrons
d. equal number of protons and neutrons

1. the whole number that is closest to the atomic mass of an atom is the

a. atomic number
b. mass number
c. avogadros number
d. number of neutrons

1. the ion with the charge of + 1 and the same electron configuration as argon is

a. potassium
b. sodium
c. neon
d. magnesium

1. the tendency to lose electrons ________ as we move across a period on the periodic table

a. increases
b. remains the same
c. decreases
d. no trend exists

1. atomic radii generally increases in size from ________ in the periodic table

a. up a group and left to right across a period
b. down a group and left to right across a period
c. up a group and right to left across a period
d. down a group and right to left across a period

1. the ________ generally have the lowest ionization energy

a. noble gases
b. metalloids
c. nonmetals
d. metals

Explanation:

Step1: Recall atomic - structure relationships

The atomic number (Z) is equal to the number of protons and for a neutral atom, the number of electrons. The mass number (A) is the sum of protons and neutrons (A = p + n).

Step2: Solve for number of sub - atomic particles in question 1

Given atomic number Z = 48, so number of protons = 48 and number of electrons = 48. Mass number A = 120, number of neutrons n=A - p=120 - 48 = 72. So the atom contains 48 protons, 48 electrons, 72 neutrons.

Step3: Identify the element in question 2

Mass number A = 23, number of neutrons n = 12. Number of protons p=A - n=23 - 12 = 11. The element with atomic number 11 is sodium.

Step4: Recall properties of the nucleus

The nucleus contains protons (positively charged) and neutrons (neutral), so it has a positive charge and high density.

Step5: Define an ion

An ion is formed when an atom gains or loses electrons. So an ion always has an unequal number of protons and electrons.

Step6: Recall atomic mass concepts

The atomic mass is closest to the mass number. The atomic number is just the number of protons, Avogadro's number is \(6.022\times 10^{23}\), and number of neutrons is just one part of the mass - number calculation.

Step7: Determine the ion in question 6

Argon has 18 electrons. An ion with a + 1 charge and 18 electrons has 19 protons, which is potassium.

Step8: Recall periodic trends in electron - losing tendency

As we move across a period, the tendency to lose electrons decreases because the effective nuclear charge increases and the electrons are held more tightly.

Step9: Recall periodic trends in atomic radius

Atomic radii generally increase down a group and right to left across a period.

Step10: Recall ionization energy trends

Metals generally have the lowest ionization energy as they tend to lose electrons easily.

Answer:

1. a. 48 protons, 48 electrons, 72 neutrons
2. d. Sodium
3. a. a high density
4. a. unequal number of protons and electrons
5. b. mass number
6. a. potassium
7. c. decreases
8. d. down a group and right to left across a period
9. d. metals