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General Chemistry: Atoms and Elements

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  • What does the Law of Conservation of Mass state?

    Mass is neither created nor destroyed in a chemical reaction; the total mass of reactants equals the total mass of products.

  • What is the Law of Definite Proportions?

    A chemical compound always contains the same elements in the exact same proportion by mass, regardless of sample size.

  • What does the Law of Multiple Proportions state?

    When two elements form more than one compound, the masses of one element that combine with a fixed mass of the other are in small whole-number ratios.

  • What was John Dalton's contribution to atomic theory?

    Dalton proposed that matter is made of indivisible atoms, atoms of an element are identical, and atoms combine in simple whole-number ratios to form compounds.

  • What did J.J. Thomson discover about the atom?

    Thomson discovered the electron and proposed the plum pudding model where electrons are embedded in a positive sphere.

  • What was Ernest Rutherford's key discovery?

    Rutherford discovered the nucleus by gold foil experiment, showing atoms have a dense positive center with electrons around it.

  • What did Robert Millikan measure?

    Millikan measured the charge of the electron using the oil drop experiment, allowing calculation of the electron's mass.

  • What is radioactivity?

    Radioactivity is the spontaneous emission of particles or energy from an unstable atomic nucleus.

  • What are the three main subatomic particles?

    Protons (positive charge), neutrons (neutral), and electrons (negative charge).

  • What defines an isotope?

    Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons.

  • How is the periodic table organized?

    Elements are arranged by increasing atomic number and grouped by similar chemical properties in columns called groups.

  • What are ions?

    Ions are atoms or molecules with a net electric charge due to loss or gain of electrons.

  • How does the periodic table relate to ion formation?

    Elements in the same group tend to form ions with the same charge due to similar valence electron configurations.

  • What is average atomic mass?

    The weighted average mass of an element's isotopes based on their natural abundance.

  • What is a mole in chemistry?

    A mole is the amount of substance containing exactly \(6.022\times10^{23}\) entities (Avogadro's number).

  • What is Avogadro's number?

    6.022 × 1023, the number of particles in one mole of a substance.

  • What is molar mass?

    The mass of one mole of a substance, usually expressed in grams per mole (g/mol).

  • How do you calculate average atomic mass?

    Multiply each isotope's mass by its fractional abundance and sum the results.

  • What is the charge and location of a proton?

    Protons have a +1 charge and are located in the nucleus of the atom.

  • Where are electrons found in an atom?

    Electrons have a -1 charge and are found in the electron cloud surrounding the nucleus.

  • What is the significance of neutrons in the nucleus?

    Neutrons have no charge and contribute to the mass and stability of the nucleus.