Atomic Structure and Matter

• Matter is anything with mass that occupies space.
• Atoms are the smallest particles that constitute matter.

Atomic Structure

• The nucleus, located at the atom's center, contains protons and neutrons.
• Electrons are much smaller and lighter, existing in an electron cloud around the nucleus.
• The Bohr model, while not current, is a convenient way to represent atoms.
• Protons possess a positive charge (+) and reside in the nucleus; the number of protons defines the element.
• Neutrons have a neutral charge and are found in the nucleus alongside protons.
• A nucleus with protons and neutrons has an overall positive charge.
• Electrons are small, light, and negatively charged (-), and can be gained or lost during reactions.
• Electrons exist in a cloud, moving randomly in discrete energy levels or shells.
• Protons and neutrons have similar masses; protons have a +1 charge, while neutrons are neutral.
• Electrons have a -1 charge and are approximately 1800 times lighter than protons and neutrons.
• Atoms are neutral, with the number of electrons equaling the number of protons.
• Electrostatic attraction is the attraction between opposite charges (+/-).
• Protons and electrons attract through electrostatic attraction, while like charges (+/+ or -/-) repel via electrostatic repulsion.
• Nuclear force is a stronger force that counteracts proton repulsion in the nucleus.

Periodic Table

• Elements are arranged by increasing atomic number.
• The periodic table includes groups, periods, metals, non-metals, semi-metals, transition metals, alkali metals, noble gases, and halogens.
• Neutrons are calculated by subtracting the atomic number from the mass number: N = (P+N) – (P).

Rutherford's Experiment

• Positively charged alpha particles were aimed at gold foil, leading to three observations:
  • Most particles passed through, indicating mostly empty space.
  • Some particles were strongly deflected, indicating a positive nucleus.
  • Some particles were weakly deflected, indicating a surrounding negative electron cloud.

Elements and Compounds

• An element is a pure substance with identical atoms, each having the same number of protons.
• Elements are the basic building blocks of matter.
• An atom is the smallest unit of an element.
• A molecule consists of two or more chemically combined atoms.
• A compound consists of two or more different atoms chemically combined.
• A mixture consists of two or more elements or compounds not chemically joined; they can be separated.
• All compounds are molecules, but not all molecules are compounds.