Atoms and Molecules

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An atom is the smallest particle of an element that retains the chemical properties of that element. According to modern atomic theory, atoms contain subatomic particles: protons (positive charge), ne…

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An atomic mass unit (amu) is defined as one-twelfth of the mass of a carbon-12 atom. It is used because individual atoms are extremely small and have very small masses (around 10⁻²³ grams). Using amu …

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Relative atomic mass of Cl = (35 × 0.75) + (37 × 0.25) = 26.25 + 9.25 = 35.5 amu. This calculation considers the weighted average of both isotopes based on their natural abundance on Earth. The result…

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Isotopes are atoms of the same element that have the same atomic number (number of protons) but different mass numbers (different number of neutrons). This means they have different atomic masses. Exa…

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Carbon has two naturally occurring isotopes: C-12 (98.9% abundance) and C-13 (1.1% abundance). The atomic mass shown in the periodic table is the weighted average of these isotopes: (12 × 0.989) + (13…

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An atom is the smallest particle of an element that retains its properties. A molecule is the smallest particle of an element or compound made of two or more atoms bonded together. Key differences: (1…

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A molecule is a combination of two or more atoms held together by chemical bonds. Molecules are classified by: (1) Atomicity - number of atoms: Diatomic (2 atoms), Triatomic (3 atoms), Polyatomic (>3 …

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Relative molecular mass of H₂SO₄ = (2 × 1) + (1 × 32) + (4 × 16) = 2 + 32 + 64 = 98 amu. This means one molecule of H₂SO₄ is 98 times as heavy as 1/12th of a carbon-12 atom. If expressed as gram molec…