Mid term 2

Exothermic and Endothermic Reactions

  • Exothermic Graph: Graph representing reactions that release energy in the form of heat.

  • Endothermic Reaction: Results in a decrease in temperature and feels cool to the touch.

Atomic Composition

  • Atomic Number: Defined as the number of protons in the nucleus of an atom.

  • Example: If an atom contains 3 protons, 4 neutrons, and 3 electrons, its atomic number is 3 (equal to the number of protons).

  • Mass Number: Total number of protons and neutrons in the nucleus.

  • Example: For an atom with 11 protons, 12 neutrons, and 11 electrons, the mass number is 11 + 12 = 23.

  • Isotopes: Atoms of the same element that have the same number of protons but a different number of neutrons, resulting in different mass numbers.

  • Subatomic Particles:

    • Protons and Neutrons: Found in the nucleus of the atom.

    • Electrons: Orbit the nucleus in electron shells.

Atomic Charge and Stability

  • Ion: An atom with a different number of electrons and protons, resulting in a positive or negative charge.

    • Negative charge indicates that the atom has gained electrons.

  • Neutral Atom: Has the same number of protons and electrons.

  • Noble Gases: Have full valence electron shells and are considered stable (e.g., Helium, Neon, Argon).

Chemical Bonds

  • Covalent Bonds:

    • Formed when atoms share electrons.

    • Typically occur between two nonmetals.

    • Properties: Molecules formed by covalent bonds do not conduct electricity well.

  • Compound: A substance made up of two or more elements bonded together.

Phase Changes

  • Deposition: The process when a gas changes directly into a solid.

  • Ionization: The conversion of a solid, liquid, or gas to plasma.

Chemical and Physical Properties

  • Chemical Property: An example is flammability.

  • Physical Changes: Examples include slicing bread, water condensing and vaporizing.

  • Chemical Changes: An example includes the rusting of a metal.

Molecular Structure

  • Valence Electrons: Responsible for making chemical bonds between atoms.

  • Molecule of Water: Composed of two hydrogen atoms and one oxygen atom (H₂O).

Solutions and Mixtures

  • Suspension: A mixture that can be separated by filtration or settles upon standing.

  • Colloid: Contains intermediate-sized particles that scatter light (e.g., milk).

  • Solvent: The larger part of a solution, usually the liquid component.

  • Soluble: A substance that can dissolve in a solvent (e.g., salt in water).

Chemical Reactions

  • Reactants: The substances present before a chemical reaction occurs.

  • Activation Energy: The minimum energy required to initiate a chemical reaction.

  • Catalyst: A substance that increases the rate of a chemical reaction without being consumed in the process.

  • Law of Conservation of Mass: States that matter cannot be created or destroyed during a chemical reaction.

Atomic Models

  • Plum Pudding Model: An early model of atomic structure proposed by J.J. Thomson, depicting the atom as a sphere of positive charge with embedded electrons.

  • Rutherford's Nuclear Model: Proposed by Ernest Rutherford, it describes the atom as mostly empty space, with a dense nucleus at its center.

Chemical Reactions with Metals

  • Acids: Known to dissolve metals, demonstrating their reactive properties.