# The Periodic Table and Atoms | General Chemistry 1

The periodic table and atoms are studied in this chapter: chemical periodicity, metal vs. non-metal, groups in the periodic table and their properties, atomic mass and average atomic mass, the concept of a mole, mole number, molecular mass and molar mass

## The Periodic Table

The periodic table:

A chart of 118 elements first published by Dmitri Mendeleev in 1869, in which elements with similar chemical and physical properties are grouped. The elements are arranged by atomic number. Each vertical column corresponds to a group of elements with the same properties, each horizontal line corresponds to a period

Elements in the table

Each element of the periodic table is represented by a tile containing the name of the element (chemical symbol composed of one or two letters), the atomic number and the average mass (usually indicated with 4 significant figures)

Chemical periodicity

The chemical elements have a periodic pattern when they are arranged in ascending order of atomic number. A period forms a row of the periodic table. You should generally know the first 3 periods:

• 1st period: H, He
• 2nd period: Li, Be, B, C, N, O, F, Ne
• 3rd period: Na, Mg, Al, Si, P, S, Cl, Ar

Mnemonic Device:

Here He Lies Beneath Bed Clothes, Nothing On, Feeling Nervous, Naughty Margret Always Sighs, " Please Stop Clowning Around "

## Group Properties

Groups of the periodic table:

A vertical column of elements is called a group. There are 18 groups in total. Members of the same group have the same number of electrons in the outermost shells of their atoms and form bonds of the same type. The elements can be classified into:

• The main-group elements: elements in the 2 groups on the far left and the 6 groups on the far right of the periodic table (groups 1, 2, 13-18)
• The transition metals: elements in the groups between the elements of the main group (groups 3-12)
• The inner transition metals: elements in the 2 rows at the bottom of the table. The top-row elements are called lanthanides and the bottom-row elements are actinides

Special groups

Several groups of representative elements are known by common names:

• Alkali metals: 1st column = lithium, sodium, potassium, (rubidium, caesium and francium)
⇒ very reactive metals and can explode if they are exposed to water
• Alkaline-earth metals: 2nd column = beryllium, magnesium, calcium, (strontium, barium, radium)
⇒ react with O2, less reactive to water than alkali metals
• Halogens: penultimate column = fluorine, chlorine, bromine, iodine, (astatine)
⇒ colorful and corrosive nonmetals, very reactive
• Noble gases: last column = helium, neon, argon, (krypton, xenon, radon)
⇒ very stable elements, generally considered to be inert gases

## Metal vs. Nonmetal

Metals, nonmetals and metalloids

Most elements can be classified as metals or nonmetals based on their ability to conduct heat and electricity:

• Metal: good conductor of heat and electricity. They tend to be hard, metallic-looking solids with high melting and boiling points. The majority of elements are metals
• Nonmetal: poor conductor of heat and electricity. They are generally softer elements, often colored, with lower melting and boiling points than most metals
• Metalloid: an element with properties intermediate between metals and nonmetals. Metalloids divide the periodic table in a zigzag line between metals on the left and nonmetals on the right

Metallic trend

The metallic character is essentially the ease with which an atom gives up an electron

• Metallic character increases down a group. Going down a group, the atomic radius increases: the outer electrons are farther from the nucleus and are easier to remove, thus increasing the metallic character
• Metallic character decreases from left to right in each period of the periodic table. The outer electrons have an increasing effective nuclear charge and thus require more energy for their removal decreasing the metallic character

## Average Atomic Mass

Atomic mass unit (amu):

The mass exactly equal to one twelfth the mass of an atom of carbon-12
1 amu = 1.6605378 x 10-24 g

Atomic mass (in amu):

The atomic mass is the mass of a single atom of a chemical element in atomic mass units. It includes the masses of the 3 subatomic particles that make up an atom: protons, neutrons and electrons

Average atomic mass (in amu):

The average of the atomic masses of all natural isotopes of an element weighted by their abundance. The periodic table contains the average atomic mass of each element. For simplicity, the word 'average' is usually omitted when the atomic masses of the elements are discussed

Average atomic mass of the carbon atom:

Carbon has 2 isotopes: 12C (12.000 amu - 98.89%) and 13C (13.003 amu - 1.11%)

• The atomic mass of 12C is 12.000 amu
• The average atomic mass of carbon is 12.000 x 0.9889 + 13.003 x 0.0111 = 12.011 amu

## The Mole

Mole:

The amount of a substance that contains as many elementary entities as there are atoms in exactly 12.0 g of 12C. This quantity is used to express the number of atoms in a macroscopic sample of matter. . It represents the link between the microscopic and the macroscopic. 1 mole corresponds to 6.022 x 1023 atoms

12.0 g of 12C x  x  = 6.022 x 1023 12C atoms

The number used to convert moles in numbers of atoms. NA = 6.022 x 1023 items.mol-1

## Masses and Mole Number

Molecular mass (in amu):

The sum of the atomic masses of the atoms that make up a molecule

Molar mass M (in g.mol-1):

The mass of one mole of the substance (molecules, atoms, ions). The molar mass of an ion or a molecule is equal to the sum of the molar masses of all the atoms making up the ion or the molecule

Molecular mass of CH4 = atomic mass of carbon + 4 x atomic mass of hydrogen
= 12.01 + 4 x 1.008 = 16.04 amu

Molar mass of CH4 = molar mass of carbon + 4 x molar mass of hydrogen
MCH4 = MC + 4 MH = 12.01 + 4 x 1.008 = 16.04 g.mol-1

Mole number n (in mol):

The number of moles in a sample

m = mass of the substance (in g)
M = molar mass of the substance (in g.mol-1)

N = number of particles in the sample
NA = Avogadro’s number (in mol-1)

The periodic table is a chart of 118 elements first published by Dmitri Mendeleev in 1869, in which elements with similar chemical and physical properties are grouped. The elements are classified by atomic number. Each vertical column corresponds to a group of elements with the same properties, each horizontal line corresponds to a period

Scientists use the periodic table to quickly refer to information about an element, such as atomic mass and chemical symbol. The arrangement of the periodic table also allows scientists to discern trends in the properties of éléments, such as electronegativity, ionization energy, and atomic radius

A period is a horizontal row in the periodic table while a group is a column. Members of the same group have the same number of electrons in the outermost shells of their atoms and form bonds of the same type. There are a total of 18 groups

Use a mnemonic device to help you remember the order of the elements. Create a sentence that you can remember using the first letters or symbols of the elements

Mnemonic device for the first 3 periods:

Here He Lies Beneath Bed Clothes, Nothing On, Feeling Nervous, Naughty Margret Always Sighs, " Please Stop Clowning Around "

There are 18 groups in the periodic table. From left to right, there are 2 groups of elements in the s-block (alkali metals and alkaline earth metals), 10 groups in the d-block (transition block) and 6 groups in the p-block (main block)

A main group element is an element belonging to the s- and p-blocks of the periodic table (groups 1, 2, 13-18)

Transition elements are elements found in groups 3 to 12 of the periodic table corresponding to the d-block

There are 4 special families in the periodic table: the alkali metals (group 1), the alkaline-earth metals (group 2), the halogens (group 17), and the noble gases (group 18)

Metals are good conductors of heat and electricity. They tend to be hard, metallic-looking solids with high melting and boiling points. Nonmetals are poor conductors of heat and electricity. They tend to be softer, often colored elements, with lower melting and boiling points than most metals

A metalloid is an element with properties intermediate between metals and nonmetals. Metalloids are also called semimetals

The 8 metalloid elements are, in ascending order of atomic number, boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), tellurium (Te), polonium (Po), and tennessine (Ts). The metalloids divide the periodic table in a zig-zag between metals on the left and nonmetals on the right

The metallic character increases as one moves down a group. The metallic character is essentially the ease with which an atom gives up an electron. The atomic radius increases as one moves down the group: the outer electrons are further from the nucleus and are easier to remove, which increases the metallic character

The metallic character decreases from left to right in each period of the periodic table. Indeed, the outer electrons have an increasing effective nuclear charge and thus require more energy for their removal, which decreases their metallic character

A mole in chemistry is the amount of a substance that contains as many elementary entities as there are atoms in exactly 12.0 g of 12C

1 mole corresponds to 6.022 x 1023 atoms

The mole is used in chemistry to express the number of atoms in a macroscopic sample of matter. It represents the link between the microscopic and the macroscopic

Atomic mass is the mass of a single atom of a chemical element, while molecular mass is the sum of the atomic masses of the atoms that make up a molecule

Molecular mass is the sum of the atomic masses of the atoms that make up a molecule, whereas molar mass is the mass of one mole of the substance (molecules, atoms, ions)

The molar mass of an ion or molecule is equal to the sum of the molar masses of all the atoms making up the ion or molecule

Molar mass of CH4 = molar mass of carbon + 4 x molar mass of hydrogen
MCH4 = MC + 4 MH = 12.01 + 4 x 1.008 = 16.04 g.mol-1

The number of moles in a sample is equal to the mass of the sample divided by the molar mass of the substance:

n = $\frac{\mathrm{m}}{\mathrm{M}}$

m = mass of the substance (in g)
M = molar mass of the substance (in g.mol-1)

The number of moles in a sample is equal to the number of particles in the sample divided by the Avogadro's number:

n = $\frac{\mathrm{N}}{{\mathrm{N}}_{\mathrm{A}}}$

N = number of particles in the substance
NA = Avogadro’s number (in mol-1)