Difficulty: Introductory | Prerequisites: None, though familiarity with basic atomic structure (protons, neutrons, electrons) helps.
The periodic table is the organising framework for all of chemistry. It arranges every known element by atomic number and groups them so that elements in the same column share similar chemical behaviour. This topic sits right at the start of most general chemistry courses because nearly everything that follows, from bonding to reactions to thermodynamics, relies on understanding where an element sits on the table and what that position tells you about its properties. You should already be comfortable with the idea that atoms have protons, neutrons and electrons, but no prior chemistry coursework is assumed.
The periodic table sorts elements by atomic number into rows (periods) and columns (groups). Elements in the same group have the same number of valence electrons and behave similarly. The three broad categories, metals, nonmetals and metalloids, differ in their physical properties (lustre, conductivity, malleability) and in how readily they gain or lose electrons.
Periodic law
The chemical and physical properties of elements repeat in a predictable pattern when the elements are arranged by increasing atomic number. In simple terms, this means that if you line up the elements by how many protons they have, their behaviour cycles in a regular way.
Period
A horizontal row on the periodic table. Each period represents a new principal energy level being filled with electrons. Think of it as one lap across the table before dropping down to a new shell.
Group (family)
A vertical column on the periodic table. Elements in the same group share the same number of valence electrons and, consequently, similar chemical properties. In simple terms, groups are like columns of relatives who behave alike.
Valence electrons
The electrons in an atom's outermost energy level, the ones involved in bonding and chemical reactions. These are the highest-energy electrons and they determine how an element reacts. Think of them as the electrons that are "available" for chemistry.
Atomic number (Z)
The number of protons in an atom's nucleus. It defines which element an atom is and determines its position on the periodic table.
Metal
An element that is typically lustrous, malleable, ductile and a good conductor of heat and electricity. Metals tend to lose electrons easily. Think of them as the elements that would rather give electrons away than hold on to them.
Nonmetal
An element that is typically brittle (if solid), dull, and a poor conductor. Nonmetals tend to gain electrons. In simple terms, these are the elements that grab onto extra electrons rather than letting go of their own.
Metalloid (semimetal)
An element with properties intermediate between metals and nonmetals, found along the "staircase" line on the periodic table. Their reactivity depends on what they are reacting with. Think of them as the elements that can swing either way, depending on the circumstances.
Elements are arranged in order of increasing atomic number (number of protons)
Periods (rows): each new row corresponds to a new principal energy level (n = 1, 2, 3, etc.)
Groups (columns): elements in the same column share the same valence electron configuration
The Roman numeral of a main-group column tells you how many valence electrons those elements have
Example: Group VA elements each have five valence electrons
Valence electrons are the outermost, highest-energy electrons and are the ones responsible for chemical bonding
The periodic law underpins the whole layout: properties repeat at regular intervals when elements are listed by atomic number
Metals
Found on the left and centre of the periodic table (the majority of elements)
Lustrous (shiny) solids at room temperature, except mercury, which is a liquid
Generally high melting points and densities
Malleable (can be hammered into sheets) and ductile (can be drawn into wires)
Good conductors of heat and electricity
Electropositive: low nuclear charge on valence electrons, so they give up electrons easily
Large atomic radius, small ionic radius (because the cation has fewer electrons than the neutral atom)
Low ionization energy and low electron affinity
Nonmetals
Clustered in the upper right of the periodic table
Generally brittle (if solid), with little to no metallic lustre
Poor conductors of heat and electricity
High ionization energy, high electron affinity, high electronegativity
Small atomic radii, large ionic radii (the anion has more electrons than the neutral atom)
Tend to gain electrons rather than lose them
Metalloids (semimetals)
Sit along the "staircase" diagonal line that separates metals from nonmetals
Properties are intermediate: electronegativity and ionization energy fall between those of metals and nonmetals
Reactivity depends on the element they are reacting with, so they can behave as either metals or nonmetals depending on context
The commonly recognised metalloids are: B, Si, Ge, As, Sb, Te, Po, At
Silicon is the most commercially important metalloid, used extensively in semiconductors
The metal/nonmetal distinction is why copper wires carry your electricity (metal, good conductor) while the rubber coating around them keeps you safe (nonmetal polymer, poor conductor). Metalloids like silicon sit right at the boundary, which is precisely what makes them useful as semiconductors: their conductivity can be tuned, and that tunability is the basis of every computer chip and solar cell.
Students often think "metalloid" means "a little bit metal." It does not. Metalloids have genuinely intermediate properties and can act as either metals or nonmetals depending on the reaction partner.
Students sometimes assume all metals are hard, heavy solids. They are not. Sodium is soft enough to cut with a knife, lithium floats on water, and mercury is a liquid at room temperature.
The staircase line on the periodic table is sometimes treated as a sharp boundary. It is better understood as a rough guide: elements near it can show mixed behaviour.
Students frequently confuse "group" and "period." A group is a column (vertical), a period is a row (horizontal). The group number tells you the valence electron count for main-group elements.
⚠️ Know the difference between groups and periods, and be able to identify each by number or letter designation (IA, IIA, etc.).
⚠️ Be able to classify any element as a metal, nonmetal or metalloid given its position on the table.
⚠️ Expect questions that ask you to predict physical properties (conductivity, malleability, lustre) from an element's classification.
⚠️ The metalloid list (B, Si, Ge, As, Sb, Te, Po, At) comes up regularly. Memorise it.
⚠️ Understand that the Roman numeral group number equals the number of valence electrons for main-group (A) elements.
True or false: elements in the same period have the same number of valence electrons.
Fill in the blank: a vertical column on the periodic table is called a ______.
True or false: mercury is a metal even though it is a liquid at room temperature.
Fill in the blank: metalloids are found along the ______ on the periodic table.
True or false: nonmetals are generally good conductors of electricity.
Answers: 1. False (same group, not same period). 2. Group (or family). 3. True. 4. Staircase (diagonal line). 5. False.
Q: What does the periodic law state, and how is it reflected in the layout of the periodic table?
A: The periodic law states that the chemical and physical properties of elements are periodic functions of their atomic numbers. The table reflects this by arranging elements in order of increasing atomic number so that elements with similar properties fall into the same vertical group.
Q: An element is shiny, conducts electricity well, and can be drawn into a wire. Is it most likely a metal, nonmetal or metalloid? Explain.
A: It is most likely a metal. Lustre, electrical conductivity and ductility (ability to be drawn into wire) are characteristic metal properties.
Q: Silicon is classified as a metalloid. Why is it useful in electronics?
A: Because its conductivity is intermediate between metals and nonmetals, silicon can be "doped" to control how well it conducts. This tunability makes it the foundation of semiconductor devices.
Q: How can you determine the number of valence electrons for a main-group element from the periodic table?
A: The Roman numeral of the element's group (column) gives the number of valence electrons. For example, Group VA elements have five valence electrons.
Q: Name three metalloids.
A: Any three of: boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), tellurium (Te), polonium (Po), astatine (At).
This material connects directly to periodic trends (ionization energy, electron affinity, electronegativity, atomic radius), which are covered in Part 2 of these notes. Understanding where metals and nonmetals sit on the table is essential for predicting ionic vs. covalent bonding later in the course. The group chemistry section (Part 3) builds on the element-type classifications introduced here by looking at specific families such as alkali metals, halogens and noble gases.
Periodic table, periodic law, periods, groups, families, columns, rows, valence electrons, metals, nonmetals, metalloids, semimetals, staircase line, malleable, ductile, lustrous, conductors, insulators, electropositive, atomic number, element classification, main-group elements, representative elements, periodic table organisation