Chemical Bonding Basics
Grade 8 · Science · Study Guide
Understand how atoms join together through ionic, covalent, and metallic bonds to form compounds.
Chemical bonds are forces that hold atoms together to form compounds. Atoms bond because doing so makes them more stable — most atoms seek a full outermost electron shell, typically 8 electrons (the octet rule).
Ionic bonds form when one atom transfers electrons to another. This usually happens between a metal and a nonmetal. The atom that loses electrons becomes a positively charged ion (cation), and the atom that gains electrons becomes a negatively charged ion (anion). The opposite charges attract each other, forming an ionic bond. Table salt (NaCl) is a classic example: sodium gives one electron to chlorine.
Covalent bonds form when two atoms share electrons rather than transfer them. This typically occurs between two nonmetals. Water (H₂O) and carbon dioxide (CO₂) are common covalent compounds. A single covalent bond shares one pair of electrons; a double bond shares two pairs.
Metallic bonds occur between metal atoms. Electrons are not held by any one atom but move freely in a "sea of electrons." This explains why metals conduct electricity and heat well and are malleable.
The type of bond formed determines the properties of the resulting compound — such as melting point, conductivity, and solubility.
Key terms
- Ionic bond
- A chemical bond formed by the transfer of electrons from one atom to another, creating oppositely charged ions that attract
- Covalent bond
- A chemical bond formed when two atoms share one or more pairs of electrons
- Octet rule
- The tendency of atoms to form bonds so that each atom has 8 electrons in its outermost shell
- Ion
- An atom or molecule that has gained or lost electrons, giving it a positive or negative charge
- Metallic bond
- A bond formed by the attraction between positively charged metal ions and the surrounding sea of free electrons
- Valence electrons
- The electrons in the outermost shell of an atom that are involved in forming chemical bonds
Flashcards
- Cation
- A positively charged ion formed when an atom loses one or more electrons
- Anion
- A negatively charged ion formed when an atom gains one or more electrons
- Compound
- A pure substance formed when two or more elements are chemically bonded together
- Diatomic molecule
- A molecule made of two atoms of the same element bonded together, such as O₂ or N₂
- Double bond
- A covalent bond in which two pairs of electrons are shared between two atoms
- Octet rule
- Atoms tend to form bonds to achieve 8 electrons in their outermost shell, like noble gases
- Electronegativity
- A measure of how strongly an atom attracts shared electrons in a bond
Questions
What type of bond is formed between sodium (Na) and chlorine (Cl) in table salt?
- Covalent bond
- Metallic bond
- Ionic bond
- Hydrogen bond
Show answer
Answer: Ionic bond
NaCl is an ionic compound: sodium transfers one electron to chlorine, forming Na⁺ and Cl⁻ ions attracted by opposite charges.
In a covalent bond, one atom completely transfers electrons to another atom.
Show answer
Answer: False
In a covalent bond, electrons are shared between atoms — not transferred. Electron transfer characterizes ionic bonds.
The electrons in the outermost shell of an atom that participate in bonding are called ______ electrons.
Show answer
Answer: valence
Valence electrons are in the outermost energy level and determine an atom's bonding behavior and chemical properties.
Which property of metals is best explained by the sea of electrons in metallic bonding?
- High melting point only
- Brittleness
- Electrical conductivity
- Transparency
Show answer
Answer: Electrical conductivity
The delocalized 'sea' of freely moving electrons allows metallic substances to conduct electricity and heat efficiently.
Water (H₂O) is held together by ionic bonds.
Show answer
Answer: False
Water is a covalent compound. Oxygen and hydrogen share electrons rather than transfer them, forming polar covalent bonds.
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