Fundamentals of Chemistry: Elements, Atomic Structure, and Electron Energy Levels

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1.1 Chemistry and Chemicals

Introduction to Chemistry

Chemicals are substances that have the same composition wherever found.
Chemistry is the study of the composition, structure, and reaction of matter.
Chemistry solves problems from a chemical perspective, helping us understand the properties and changes of substances.

4.1 Elements and Symbols

Elements and the Periodic Table

All matter is composed of 118 different elements.
Pure substances from which all other substances are built.
88 out of the 118 occur naturally in nature.
Elements cannot be broken down into simpler substances by chemical means.
An element symbol represents an element; if an element has been listed first, it is lower case (e.g., Co for cobalt, CO for carbon monoxide).

Organization of the Periodic Table

Elements are organized into groups with similar properties.
Groups (columns) contain elements with similar properties in vertical columns.
Rows (periods) are horizontal and represent elements from top to bottom.
Group numbers are written at the top of each vertical column.
Use letter A for representative elements (Groups 1A-8A).
Use letter B for transition elements (Groups 3B-8B, 1B, 2B).
The periodic table uses numbers 1-18 for all groups, from left to right.

Major Groups in the Periodic Table

Group 1A (Alkali metals): Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), Cesium (Cs). Highly reactive, especially with water.
Group 2A (Alkaline earth metals): Beryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr), Barium (Ba), Radium (Ra). Less reactive than alkali metals.
Group 7A (Halogens): Fluorine (F), Chlorine (Cl), Bromine (Br), Iodine (I), Astatine (At), Tennessine (Ts). Very reactive nonmetals.
Group 8A (Noble gases): Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe), Radon (Rn), Oganesson (Og). Inert gases, very low reactivity.

Classification of Elements

Metals: Located on the left side of the periodic table. Shiny, ductile, conduct heat and electricity, mostly solids (except mercury).
Nonmetals: Located on the right side. Dull, brittle, poor conductors, good insulators, low densities and melting points.
Metalloids: Along the zigzag line. Exhibit properties of both metals and nonmetals, used as semiconductors and insulators.

4.2 Atoms and Atomic Theory

Definition of an Atom

An atom is the smallest particle of an element that retains the characteristics of that element.

Dalton's Atomic Theory (1808)

All matter is made up of tiny particles called atoms.
Atoms of an element are the same and different from those of other elements.
Atoms of two or more different elements combine to form compounds.
A given compound has a constant composition.
Atoms are combined, separated, or rearranged in chemical reactions.
Atoms are never created or destroyed during a chemical reaction.

Discovery of Subatomic Particles

Electrons: Negatively charged particles discovered by J.J. Thomson (1897).
Protons: Positively charged particles found in the nucleus.
Neutrons: Neutral particles found in the nucleus (discovered by James Chadwick, 1932).

Structure of the Atom

Nucleus: Located at the center, contains protons and neutrons.
Electrons: Occupy a large, empty space around the nucleus.

Mass of the Atom

Chemists use a very small unit of mass called the atomic mass unit (amu).
1 amu = 1/12 of the mass of the carbon-12 atom.
Protons and neutrons each have a mass of approximately 1 amu.
Electrons have such a small mass that they are not included in the mass of an atom.

4.4 Atomic Number and Mass Number

Atomic Number

All atoms of the same element have the same number of protons and the same atomic number.
Atomic number appears above the symbol of an element in the periodic table.
It is unique for each element and helps to identify it.
For a neutral atom, the number of protons equals the number of electrons.

Mass Number

Represents the total number of particles in the nucleus (protons + neutrons).
Always a whole number, but does not appear in the periodic table.

Charge of Atoms

Atoms are neutral when the number of protons equals the number of electrons.
If the number of protons does not equal the number of electrons, the atom is an ion.
Cation: Positive charge (more protons than electrons).
Anion: Negative charge (more electrons than protons).

4.5 Isotopes and Atomic Mass

Isotopes

Atoms of the same element with the same number of protons but different numbers of neutrons.
Isotopes have different mass numbers and are distinguished by their atomic symbols.

Average Atomic Mass

The atomic mass in the periodic table is the weighted average of different isotopes.

Isotope Symbol	Mass (amu)	Abundance (%)	Contribution to Atomic Mass
24Mg	23.99	78.70	18.88 amu
25Mg	24.99	10.13	2.531 amu
26Mg	25.98	11.17	2.902 amu

To calculate average atomic mass:
1. Use experimental percent abundance of each isotope of the element.
2. Multiply the percent abundance by the atomic mass of that isotope.
3. Sum the total mass of all isotopes.

Formula:

4.6 Electron Energy Levels

Electromagnetic Radiation

Electrons emit energy called electromagnetic radiation.
Consists of energy "particles" that move as waves.
Distance between peaks is called the wavelength; short wavelengths have high energy, long wavelengths have low energy.

Type of Radiation	Wavelength	Energy
Gamma Rays	Shortest	Highest
X-Rays	Short	High
Ultraviolet	Medium	Medium
Visible Light	Longer	Lower
Microwaves	Long	Low
Radio Waves	Longest	Lowest

Atomic Spectrum

When light from a heated element passes through a prism, it separates into distinct lines of color called the atomic spectrum.
Each element has its own unique atomic spectrum.

Electron Energy Levels

Electrons in an atom are associated with changes in energy levels.
Each electron has a specific energy, known as its energy level.
Each energy level consists of one or more sublevels (orbitals).
The number of sublevels in an energy level is equal to the principal quantum number (n).
If n=1, there is only 1 sublevel; if n=2, there are 2 sublevels, etc.
The sublevels are identified as s, p, d, and f.
The order of the sublevels in an energy level is: s < p < d < f (1,3,5,7).

Characteristics of Orbitals

Orbitals are three-dimensional volumes in which electrons have the highest probability of being found.
s orbitals are spherical; p orbitals are dumbbell-shaped; d orbitals have more complex shapes.
There is one s orbital in every energy level (n=1).
There are three p orbitals starting with energy level 2 (n=2).
There are five d orbitals starting with energy level 3 (n=3).

Number of Electrons in Sublevels

Each s sublevel has 1 orbital and can hold a maximum of 2 electrons.
Each p sublevel has 3 orbitals and can hold a maximum of 6 electrons.
Each d sublevel has 5 orbitals and can hold a maximum of 10 electrons.
Each f sublevel has 7 orbitals and can hold a maximum of 14 electrons.

Sublevel	Number of Orbitals	Maximum Number of Electrons
s	1	2
p	3	6
d	5	10
f	7	14

Electron Configuration Example

Ground-state electron configuration for Carbon:
1s2 2s2 2p2 (read as "one s two, two s two, two p two")

Additional info: These notes provide foundational concepts in GOB Chemistry, including atomic structure, periodic table organization, isotopes, atomic mass, and electron energy levels, which are essential for understanding chemical properties and reactions.