# 3: Atoms and Elements

## The Nuclear Atom

Exercise $$\PageIndex{1.a}$$

How are electrons and protons similar? How are they different?

Both are subatomic particles. Protons are positively charged, and reside in an atom’s nucleus. Whereas, electrons are negatively charged and reside outside an atom’s nucleus.

Exercise $$\PageIndex{1.b}$$

How are protons and neutrons similar? How are they different?

Both are subatomic particles that reside in an atom’s nucleus. Both have approximately the same mass. Protons are positively charged, whereas neutrons are uncharged.

## The Elements

Exercise $$\PageIndex{2.a}$$

Name the following element

Ra, Rn, Mg & Mn

Exercise $$\PageIndex{2.b}$$

Name the following element

Pb, Pa, Pu, Pt & Po

Exercise $$\PageIndex{2.c}$$

Name the following elements in order

Ti, Te, Tl & At

Titanium, Tellurium, Thallium and Astatine

## Isotopes

Exercise $$\PageIndex{3.a}$$

Write the symbol for each of the following ions:

1. the ion with a 1+ charge, atomic number 55, and mass number 133
2. the ion with 54 electrons, 53 protons, and 74 neutrons
3. the ion with atomic number 15, mass number 31, and a 3− charge
4. the ion with 24 electrons, 30 neutrons, and a 3+ charge

(see

133Cs+

127I

31P3+

57Co3+

Exercise $$\PageIndex{3.b}$$

The following are properties of isotopes of two elements that are essential in our diet. Determine the number of protons, neutrons and electrons in each and name them.

1. atomic number 26, mass number 58, charge of 2+
2. atomic number 53, mass number 127, charge of 1−

Iron +2 cation, 26 protons, 24 electrons, and 32 neutrons (it is actually the ferrous ion, section 4.5.3.1.1.2)

Iodine -1 anion, 53 protons, 54 electrons, and 74 neutrons (it is actually the iodide ion, section 4.5.3.1)

Exercise $$\PageIndex{3.c}$$

Give the number of protons, electrons, and neutrons in neutral atoms of each of the following isotopes:

1. $$_{3}^{7}\textrm{Li}$$
2. $$_{52}^{125}\textrm{Te}$$
3. $$_{47}^{109}\textrm{Ag}$$
4. $$_{7}^{15}\textrm{N}$$
5. $$_{15}^{31}\textrm{P}$$

3 protons, 3 electrons, 4 neutrons

52 protons, 52 electrons, 73 neutrons

47 protons, 47 electrons, 62 neutrons

7 protons, 7 electrons, 8 neutrons

15 protons, 15 electrons, 16 neutrons

Exercise $$\PageIndex{3.d}$$

Write a symbol for each of the following neutral isotopes. Include the atomic number and mass number for each.

1. the alkali metal with 11 protons and a mass number of 23
2. the noble gas element with and 75 neutrons in its nucleus and 54 electrons in the neutral atom
3. the isotope with 33 protons and 40 neutrons in its nucleus
4. the alkaline earth metal with 88 electrons and 138 neutrons

$$_{11}^{23}\textrm{Na}$$

$$_{54}^{129}\textrm{Xe}$$

$$_{33}^{73}\textrm{As}$$

$$_{88}^{226}\textrm{Ra}$$

## Isotopic Abundance

Exercise $$\PageIndex{4.a}$$

Average atomic masses listed by IUPAC are based on a study of experimental results. Bromine has two isotopes 79Br and 81Br, whose masses (78.9183 and 80.9163 amu) and abundances (50.69% and 49.31%) were determined in earlier experiments. Calculate the average atomic mass of bromine based on these experiments.

 Isotope Mass Percent Abundance Fraction 79Br 78.9183amu 50.69% 0.5069 81Br 80.9163 amu 49.31% 0.4931

${X_A}{(m_A)} +{X_B}{(m_B)} = {m_{ave}}$

${X_{79Br}}{(m_{79Br})} +{X_{81Br}}{(m_{81Br})} = {m_{ave}}$

${0.5069}{(78.9183amu)} +{0.4931}{(80.9163 amu)} = {m_{ave}}$

${m_{ave}}=79.904 amu$

Exercise $$\PageIndex{4.b}$$

Average atomic masses listed by IUPAC are based on a study of experimental results. The average atomic mass of Copper is 63.546 amu. Copper has two isotopes 63Cu and 65Cu. The mass of 63Cu was determined in an earlier experiment and found to be 62.930 amu. The abundance of 63Cu was found to be 69.17%. Calculate the mass and abundance of 65Cu.

 Isotope Mass Percent Abundance Fraction 63Cu 62.930 amu 69.17% 0.6917 65Cu $$m_B\nonumber$$ $$%_B\nonumber$$ $$X_B\nonumber$$

$X_A + X_B=1$

$X_B=1-X_A$

$X_B=1-0.6917=0.3083=30.83%$

${X_A}{(m_A)} +{X_B}{(m_B)} = {m_{ave}}$

$m_B=\frac{m_{ave}-X_A(m_A)}{X_B}$

$m_B=\frac{63.546amu-0.6917(62.930 amu)}{0.3083}$

$m_B= 64.928amu$

Exercise $$\PageIndex{4.c}$$

Average atomic masses listed by IUPAC are based on a study of experimental results. The average atomic mass of Gallium is 69.723 amu. Gallium has two isotopes 69Ga and 71Ga, whose masses (68.9257 and 70.9249 amu) were determined in earlier experiments. What is the natural abundance of each isotope?

 Isotope Mass Fraction 69Ga 68.9257 amu $$X_A\nonumber$$ 71Ga 70.9249 amu $$X_B\nonumber$$

${X_A}{(m_A)} +{X_B}{(m_B)} = {m_{ave}}$

$X_A + X_B=1$

$X_B=1-X_A$

${X_A}{(m_A)} +{1-X_A}{(m_B)} = {m_{ave}}$

${X_A}=\frac{m_{ave}-m_B}{m_A-m_B}$

${X_A}=\frac{69.723 amu-70.9249amu}{68.9257amu-70.9249amu}$

${X_A}=0.6012$

$X_B=1-X_A$

$X_B=1-0.6012=0.3988$

The natural abundance of 69Ga is 60.12% and of 71Ga is 39.88%

Exercise $$\PageIndex{4.d}$$

In an alternate universe on the planet Htrae, the element Minebro has two isotopes 79Mr and 81Mr, whose masses (78.9183 and 80.9163 amu) and abundances (49.31% and 50.69%) were determined in earlier experiments. Calculate the average atomic mass of Minebro based on these experiments.

 Isotope Mass Percent Abundance Fraction 79Br 78.9183amu 49.31% 0.4931 81Br 80.9163 amu 50.69% 0.5069

${X_A}{(m_A)} +{X_B}{(m_B)} = {m_{ave}}$

${X_{79Br}}{(m_{79Br})} +{X_{81Br}}{(m_{81Br})} = {m_{ave}}$

${0.4931}{(78.9183amu)} +{0.5069}{(80.9163 amu)} = {m_{ave}}$

${m_{ave}}= 79.931amu$

Exercise $$\PageIndex{4.e}$$

In an alternate universe on the planet Htrae, the element Robber has an average atomic mass of 64.494 amu. Robber has two isotopes 63Ru and 65Ru. The mass of 63Ru was determined in an earlier experiment and found to be 62.930 amu. The abundance of 63Ru was found to be 21.72%. Calculate the mass and abundance of 65Ru.

 Isotope Mass Percent Abundance Fraction 63Cu 62.930 amu 21.72% 0.2172 65Cu $$m_B\nonumber$$ $$%_B\nonumber$$ $$X_B\nonumber$$

$X_A + X_B=1$

$X_B=1-X_A$

$X_B=1-0.2172=0.7828=78.28%$

${X_A}{(m_A)} +{X_B}{(m_B)} = {m_{ave}}$

$m_B=\frac{m_{ave}-X_A(m_A)}{X_B}$

$m_B=\frac{64.494amu-0.2172(62.930 amu)}{0.7828}$

$m_B= 64.928$

## Periodic Table

Exercise $$\PageIndex{5.a}$$

Using the periodic table, classify each of the following elements as a metal or a nonmetal, and then further classify each as a main-group (representative) element, transition metal, or inner transition metal:

1. uranium
2. bromine
3. strontium
4. neon
5. gold
6. americium
7. rhodium
8. sulfur
9. carbon
10. potassium

metal, inner transition metal

nonmetal, representative element

metal, representative element

nonmetal, representative element

metal, transition metal

metal, inner transition metal

metal, transition metal

nonmetal, representative element

nonmetal, representative element

metal, representative element

Exercise $$\PageIndex{5.b}$$

Using the periodic table, identify the lightest and heaviest member of each of the following groups:

1. noble gases
2. alkaline earth metals
3. alkali metals
4. chalcogens

He, Og

Be, Ra

Li, Fr

O, Lv

Exercise $$\PageIndex{5.c}$$

Use the periodic table to give the name and symbol for each of the following elements:

1. the noble gas in the same period as germanium
2. the alkaline earth metal in the same period as selenium
3. the halogen in the same period as lithium
4. the chalcogen in the same period as cadmium

krypton, Kr

calcium, Ca