Untitled Quiz

Atoms and Molecules

• Atoms are the basic building blocks of all matter.
• Atoms of an element have specific properties.
• Molecules are formed when two or more atoms chemically combine.
• Molecules of a compound have a particular composition.
• Chemical reactions involve the rearrangement of atoms.
• The mass of reactants equals the mass of products in a reaction.
• Compounds always contain the same elements in fixed proportions.

Laws of Chemical Combination

• Law of Conservation of Mass: The total mass of reactants equals the total mass of products in a chemical reaction. Mass is neither created nor destroyed during a chemical reaction.
• Law of Constant Proportions: A chemical compound always contains the same elements in the same proportion by mass.

Dalton's Atomic Theory

• All matter is composed of extremely small particles called atoms.
• Atoms of an element are identical in mass and properties.
• Atoms of different elements differ in mass and properties.
• Atoms combine in simple whole number ratios to form compounds.
• Atoms are neither created nor destroyed in chemical reactions.

Symbols of Atoms

• Chemical symbols are used to represent elements.
• The first letter of a symbol is capitalized, and the second letter (if any) is lowercase.
• Some symbols are derived from the Latin names for the elements.

Atomic Mass

• The atomic mass of an element is the relative mass of an atom compared to the mass of a carbon-12 atom (taken as 12 atomic mass units).

Molecules

• A molecule is a group of two or more atoms that are chemically bonded.
• Molecules of elements consist of the same type of atoms.
• Molecules of compounds consist of different types of atoms in a definite ratio.
• Atomicity is the number of atoms present in a molecule.

Ions

• Ions are charged particles formed by loss or gain of electrons by an atom.
• Cations are positively charged ions.
• Anions are negatively charged ions.

Valency

• Valency is the combining capacity of an element.
• The valency of an element represents the number of electrons an atom needs to gain or lose to achieve a complete outermost electron shell of 8 electrons.

Chemical Formulas

• Chemical formulas show the elements present in a compound and the ratio in which they combine.
• Chemical formulas are written by combining the symbols of the elements and adding subscripts to show the number of atoms of each element per molecule.

Molecular Mass

• Molecular mass is the sum of the atomic masses of all the atoms in a molecule.

Formula Unit Mass

• Formula unit mass is the sum of the atomic masses of all the ions in one formula unit of an ionic compound

Mole Concept

• A mole is a unit used to express a large number of entities (atoms, molecules, or ions).
• 1 mole of any substance contains 6.022 x 10²³ particles, called Avogadro's number.
• Molar mass is the mass of 1 mole of a substance, numerically equal to its relative formula/molecular mass in grams.