🧪 Elements
Exploring the periodic table and element properties
What are Elements?
Elements are pure substances that cannot be broken down into simpler substances by chemical means. Each element is made up of atoms with the same number of protons. There are currently 118 known elements, organized in the periodic table.
Main Idea: Each element has a unique atomic number (number of protons) that defines its identity.
The Periodic Table
The periodic table is a systematic arrangement of elements based on their atomic number and chemical properties. It was developed by Dmitri Mendeleev in 1869.
Periodic Table Organization:
Periods (Rows)
- • Horizontal rows
- • Elements in the same period have same number of electron shells
- • The number of electron shells increase down the table
- • 7 periods total
Example - Period 2:
Li, Be, B, C, N, O, F, Ne all have 2 electron shells
• Lithium (Li): 2 shells (2,1)
• Carbon (C): 2 shells (2,4)
• Neon (Ne): 2 shells (2,8)
Groups (Columns)
- • Vertical columns
- • Elements in same group have the same number of valence electrons
- • The number of valence electrons increase to the right of the table
- • 18 groups total
Example - Group 1 (Alkali Metals):
All have 1 valence electron and similar reactivity
• Lithium (Li): 1 valence electron
• Sodium (Na): 1 valence electron
• Potassium (K): 1 valence electron
All react vigorously with water!
Element Categories
Metals
- • Good conductors of heat and electricity
- • Malleable and ductile
- • Shiny appearance
- • Left side of periodic table
- • Examples: Iron, Copper, Gold
Nonmetals
- • Poor conductors of heat and electricity
- • Brittle when solid
- • Dull appearance
- • Right side of periodic table
- • Examples: Carbon, Oxygen, Nitrogen
Metalloids
- • Properties between metals and nonmetals
- • Semi-conductors
- • Staircase line on periodic table
- • Examples: Silicon, Boron, Arsenic
Important Element Groups
Group 1: Alkali Metals
Highly reactive metals that readily lose their outer electron. They react vigorously with water.
Group 17: Halogens
Highly reactive nonmetals that readily gain an electron. They form salts with metals.
Group 18: Noble Gases
Inert gases that rarely react with other elements due to their stable electron configuration.
Element Properties
Physical Properties
- • Melting point
- • Boiling point
- • Density
- • Color
- • State at room temperature
- • Conductivity
Chemical Properties
- • Reactivity
- • Oxidation states
- • Bonding behavior
- • Electronegativity
- • Ionization energy
- • Electron affinity
Reading Element Information
Element Box Information:
Periodic Trends
Atomic Size
This is the size of an atom. Increases down a group, decreases across a period. This is becuase the number of electron shells an element has increases down the periodic table (down a group). So the element becomes bigger.
The atom becomes smaller across a period because the higher the period, the more valence electrons an element has. Thus, the more valence electrons, the more attraction there will be to the nucleus of the atom (this attraction is called nuclear charge). This attraction will squeeze the electrons to the nucleus making the atom smaller.
Ionization Energy
Ionization energy is the energy required to remove an electron from an atom. So the higher the ionization energy, the more ability it has to form an ionic bond with another element. Decreases down a group, increases across a period.
Ionization energy decreases down a group because as you go down, the outer electrons are farther from the nucleus and experience less attraction. The increased number of electron shells creates more shielding, making it easier to remove electrons.
Ionization energy increases across a period because the nuclear charge increases while the number of electron shells stays the same. This creates stronger attraction between the nucleus and outer electrons, making them harder to remove.
Electronegativity
Electronegativity is the ability of an atom to attract electrons in a covalent bond. Decreases down a group, increases across a period.
Electronegativity decreases down a group because the atomic size increases, placing the nucleus farther from bonding electrons. The increased distance reduces the nucleus's ability to attract electrons from other atoms.
Electronegativity increases across a period because the nuclear charge increases while atomic size decreases. This creates stronger attraction for electrons, making the atom more likely to gain electrons in chemical bonds.
Reactivity
Reactivity refers to how readily an element undergoes chemical reactions. Metals: increases down and left; Nonmetals: increases up and right.
For metals, reactivity increases down a group because ionization energy decreases, making it easier to lose electrons. It also increases to the left because elements have fewer valence electrons to lose.
For nonmetals, reactivity increases up a group because electronegativity increases, making it easier to gain electrons. It also increases to the right because elements are closer to having a full outer shell and need fewer electrons to achieve stability.
Lazy Read
- • Elements are pure substances with unique atomic numbers
- • The periodic table organizes elements by properties and atomic number
- • Elements are classified as metals, nonmetals, or metalloids
- • Groups have similar properties, periods show trends
- • Element properties follow predictable trends across the table
- • Each element box shows symbol, name, atomic number, and mass