Elements, Atomic Structure, and the Periodic Table: Week 2 Study Notes

4.1 Elements and Symbols

Elements

Elements are pure substances that cannot be broken down into simpler substances by chemical means. They are the fundamental building blocks of matter.

• Element: A substance made of only one type of atom.

• Each element is represented by a unique chemical symbol.

• Examples: Hydrogen (H), Oxygen (O), Sodium (Na)

Chemical Symbols

Chemical symbols are shorthand notations for elements, usually consisting of one or two letters. The first letter is always capitalized, and the second letter (if present) is lowercase.

• One-letter symbols: H (Hydrogen), N (Nitrogen), O (Oxygen), F (Fluorine), P (Phosphorus), S (Sulfur), K (Potassium)

• Two-letter symbols: Co (Cobalt), Ca (Calcium), Al (Aluminum), Si (Silicon), Cl (Chlorine)

• Some symbols are derived from Latin names, e.g., Ag (silver, argentum), Au (gold, aurum).

4.2 The Periodic Table

Structure and Organization

The periodic table organizes elements by increasing atomic number and groups elements with similar properties into columns called groups or families.

• Rows are called periods.

• Columns are called groups or families.

• Elements in the same group have similar chemical properties.

Groups and Periods

• Groups are numbered 1–18 from left to right.

• Alternative notation uses Roman numerals and letters (e.g., IA, IIA, VIIIA).

• Vertical columns = groups; horizontal rows = periods.

Group Names

• Group 1: Alkali metals

• Group 2: Alkaline earth metals

• Group 17: Halogens

• Group 18: Noble gases

Metals, Nonmetals, and Metalloids

Classification on the Periodic Table

Elements are classified as metals, nonmetals, or metalloids based on their properties and position on the periodic table.

• Metals: Located to the left of the heavy zigzag line.

• Nonmetals: Located to the right of the zigzag line.

• Metalloids: Located along the zigzag line.

Characteristics

• Metals: Shiny, ductile, malleable, good conductors of heat and electricity, high melting points.

• Nonmetals: Dull, brittle, poor conductors, low melting points.

• Metalloids: Properties intermediate between metals and nonmetals; used as semiconductors.

4.3 The Atom

Dalton's Atomic Theory

John Dalton proposed that atoms are the smallest particles of matter and that each element consists of identical atoms. Atoms combine in fixed ratios to form compounds and are not created or destroyed in chemical reactions.

• All matter is made of atoms.

• Atoms of the same element are identical.

• Atoms of different elements are different.

• Atoms combine in simple ratios to form compounds.

• Atoms are not created or destroyed in chemical reactions.

Subatomic Particles

• Protons (p+): Positive charge, located in the nucleus.

• Neutrons (n0): No charge, located in the nucleus.

• Electrons (e-): Negative charge, found outside the nucleus.

Models of the Atom

• J.J. Thomson's Plum Pudding Model: Atoms are spheres of positive charge with embedded electrons.

• Rutherford's Gold Foil Experiment: Showed that atoms have a small, dense, positively charged nucleus with electrons surrounding it.

Structure of the Atom

• Nucleus: Contains protons and neutrons.

• Electrons: Occupy a large, mostly empty space around the nucleus.

Mass of the Atom

Atomic Mass

The mass of an atom is measured in atomic mass units (amu). The atomic mass unit is defined as 1/12 the mass of a carbon-12 atom.

• 1 amu = $1.66 \times 10^{-24}$ g

• Protons and neutrons each have a mass of approximately 1 amu.

• Electrons have a much smaller mass and are usually neglected in atomic mass calculations.

Subatomic Particles Table

Particle	Symbol	Charge	Mass (amu)	Location
Proton	p+	+1	1	Nucleus
Neutron	n0	0	1	Nucleus
Electron	e-	-1	0.0005	Outside nucleus

4.4 Atomic Number and Mass Number

Atomic Number ($Z$)

The atomic number is the number of protons in the nucleus of an atom. It defines the identity of the element.

• All atoms of an element have the same atomic number.

• Atomic number appears above the element symbol in the periodic table.

$\text{Atomic Number} = \text{Number of Protons}$

Mass Number ($A$)

The mass number is the total number of protons and neutrons in the nucleus of an atom.

• Mass number is not found on the periodic table; it is specific to each isotope.

$\text{Mass Number} = \text{Number of Protons} + \text{Number of Neutrons}$

Atoms Are Neutral

• In a neutral atom, the number of protons equals the number of electrons.

• Charge balance: $\text{Number of Protons} = \text{Number of Electrons}$

Composition of Atoms Table

Element	Symbol	Atomic Number	Mass Number	Protons	Neutrons	Electrons
Hydrogen	H	1	1	1	0	1
Carbon	C	6	12	6	6	6
Oxygen	O	8	16	8	8	8
Magnesium	Mg	12	24	12	12	12
Aluminum	Al	13	27	13	14	13

4.5 Isotopes and Atomic Mass

Isotopes

Isotopes are atoms of the same element (same number of protons) that have different numbers of neutrons and therefore different mass numbers.

• Isotopes have identical chemical properties but different physical properties (such as mass).

• Example: $^{12}\text{C}$ and $^{14}\text{C}$ are both isotopes of carbon.

Atomic Symbols for Isotopes

Isotopes are represented as:

$^{A}_{Z}\text{X}$

• $A$ = mass number

• $Z$ = atomic number

• $X$ = element symbol

Isotope Table Example

Isotope	Atomic Number	Mass Number	Protons	Neutrons	Electrons
$^{16}\text{O}$	8	16	8	8	8
$^{19}\text{F}$	9	19	9	10	9
$^{52}\text{Zn}$	30	52	30	22	30

Calculating Subatomic Particles

• Number of protons: Atomic number

• Number of neutrons: Mass number - Atomic number

• Number of electrons: Atomic number (for neutral atoms)

Summary Table: Subatomic Particles

Particle	Symbol	Charge	Mass (amu)	Location
Proton	p+	+1	1	Nucleus
Neutron	n0	0	1	Nucleus
Electron	e-	-1	0.0005	Outside nucleus

Key Formulas

• $\text{Atomic Number} = \text{Number of Protons}$

• $\text{Mass Number} = \text{Number of Protons} + \text{Number of Neutrons}$

• $\text{Number of Neutrons} = \text{Mass Number} - \text{Atomic Number}$

Additional info:

• Some context and explanations have been expanded for clarity and completeness.

• Tables have been reconstructed and may include inferred or typical values for illustration.