Elements, Atomic Structure, and Periodic Trends: GOB Chemistry Study Notes

Elements and Their Symbols

Writing and Identifying Element Symbols

Each chemical element is represented by a unique one- or two-letter symbol, often derived from its English or Latin name. Recognizing these symbols is fundamental in chemistry.

• Element Symbols: The first letter is always capitalized; the second letter, if present, is lowercase (e.g., Cu for copper, Pb for lead).

• Examples:

  • Copper: Cu

  • Platinum: Pt

  • Calcium: Ca

  • Manganese: Mn

  • Iron: Fe

  • Barium: Ba

  • Lead: Pb

  • Strontium: Sr

Writing Names from Symbols

Given a chemical symbol, you should be able to write the full name of the element.

• Examples:

  • C: Carbon

  • Cl: Chlorine

  • I: Iodine

  • Se: Selenium

  • N: Nitrogen

  • S: Sulfur

  • Zn: Zinc

  • Co: Cobalt

Elements in the Body

Essential Elements and Their Symbols

Certain elements are essential for life and are commonly found in the human body. Knowing their symbols and names is important for understanding biochemistry and physiology.

• Examples:

  • Na: Sodium

  • K: Potassium

  • Ca: Calcium

  • Mg: Magnesium

  • P: Phosphorus

  • Fe: Iron

  • Mo: Molybdenum

  • Si: Silicon

Periodic Table Organization

Groups and Periods

The periodic table is organized into rows (periods) and columns (groups or families). Elements in the same group have similar chemical properties.

• Groups: Vertical columns, numbered 1-18 (or IA-VIIIA, IB-VIIIB in older notation).

• Periods: Horizontal rows, numbered 1-7.

• Examples:

  • Group 1A (1): Alkali metals

  • Group 2A (2): Alkaline earth metals

  • Group 7A (17): Halogens

  • Group 8A (18): Noble gases

Identifying Groups and Periods

• Elements containing C, N, and O are found in Period 2.

• Elements beginning with helium are in Group 8A (18) (noble gases).

• Alkali metals are in Group 1A (1).

• Elements ending with neon are in Period 2.

Element Classification

Metals, Nonmetals, and Metalloids

Elements are classified based on their physical and chemical properties.

• Metals: Shiny, good conductors of heat and electricity, malleable, ductile (e.g., calcium, silver).

• Nonmetals: Dull, poor conductors, brittle (e.g., sulfur, bromine).

• Metalloids: Properties intermediate between metals and nonmetals (e.g., boron).

Atomic Structure

Subatomic Particles

Atoms are composed of protons, neutrons, and electrons, each with distinct properties.

• Proton: Positively charged (+1), found in the nucleus, mass ≈ 1 amu.

• Neutron: No charge (neutral), found in the nucleus, mass ≈ 1 amu.

• Electron: Negatively charged (-1), found outside the nucleus, mass ≈ 1/1836 amu.

Identifying Subatomic Particles

• Smallest mass: Electron

• +1 charge: Proton

• Found outside nucleus: Electron

• Electrically neutral: Neutron

Atomic Number, Mass Number, and Isotopes

The atomic number (Z) is the number of protons in an atom. The mass number (A) is the sum of protons and neutrons.

• Atomic Number (Z): Number of protons; defines the element.

• Mass Number (A): Number of protons + neutrons.

• Isotopes: Atoms of the same element with different numbers of neutrons.

Formula:

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

Protons, Neutrons, and Electrons in Neutral Atoms

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

• Example: Argon (atomic number 18) has 18 protons and 18 electrons.

Table: Atomic Structure of Essential Elements

The following table summarizes the atomic structure of several essential elements:

Name of the Element	Symbol	Atomic Number	Mass Number	Number of Protons	Number of Neutrons	Number of Electrons
Zinc	Zn	30	66	30	36	30
Magnesium	Mg	12	24	12	12	12
Potassium	K	19	39	19	20	19
Sulfur	S	16	31	16	15	16
Iron	Fe	26	56	26	30	26

Periodic Trends

Atomic Size (Atomic Radius)

Atomic size refers to the distance from the nucleus to the outermost electron shell. It varies across periods and groups.

• Trends:

  • Increases down a group (more electron shells).

  • Decreases across a period (left to right) due to increasing nuclear charge.

• Example: Na is larger than Cl; Mg is larger than Al.

Ionization Energy

Ionization energy is the energy required to remove an electron from a gaseous atom. It indicates how strongly an atom holds onto its electrons.

• Trends:

  • Increases across a period (left to right).

  • Decreases down a group.

• Example: F has a higher ionization energy than Cl or Br.

Summary Table: Periodic Trends

Trend	Across a Period (Left to Right)	Down a Group
Atomic Size	Decreases	Increases
Ionization Energy	Increases	Decreases

Practice with Atomic Numbers and Symbols

Identifying Elements by Atomic Number

Each element has a unique atomic number, which determines its identity.

• Examples:

  • Atomic number 3: Lithium (Li)

  • Atomic number 9: Fluorine (F)

  • Atomic number 20: Calcium (Ca)

  • Atomic number 30: Zinc (Zn)

  • Atomic number 10: Neon (Ne)

  • Atomic number 14: Silicon (Si)

  • Atomic number 53: Iodine (I)

  • Atomic number 8: Oxygen (O)

Calculating Protons, Neutrons, and Electrons

Given atomic and mass numbers, you can determine the number of protons, neutrons, and electrons in a neutral atom.

• Protons: Equal to atomic number.

• Electrons: Equal to atomic number (in a neutral atom).

• Neutrons: Mass number minus atomic number.

• Example: Manganese (atomic number 25, mass number 55): 25 protons, 25 electrons, 30 neutrons.

Key Definitions

• Element: A pure substance consisting of only one type of atom.

• Atom: The smallest unit of an element that retains its chemical properties.

• Isotope: Atoms of the same element with different numbers of neutrons.

• Ionization Energy: The energy required to remove an electron from an atom in the gaseous state.

• Atomic Radius: The size of an atom, typically measured from the nucleus to the outermost electron shell.