Atoms and the Periodic Table

Atoms

  • Definition: Atoms are the simplest and smallest particles composed of:

    • Protons: Positively charged particles found inside the nucleus; this defines the atomic number.

    • Electrons: Negatively charged particles that orbit the nucleus; they also define the atomic mass.

    • Neutrons: Neutral particles located inside the nucleus; they contribute to the atomic mass but not the atomic number.

Periodic Table of Elements

  • Definition: The periodic table is an arrangement of elements based on increasing atomic number and similar properties.

  • Elements: Substances that cannot be broken down by chemical means.

  • Each element on the periodic table has the following characteristics:

    • Symbol: A one- or two-letter abbreviation of the element's name.

    • Atomic Number: The number of protons in the nucleus, which also equals the number of electrons.

    • Average Atomic Mass: The sum of protons and neutrons in the nucleus, providing the weighted average mass of the element based on the isotopes present.

Example: For Carbon:

  • Symbol: C

  • Atomic Number: 6

  • Average Atomic Mass: 12.0107

Elements Groups

  • Classification: Elements are grouped by their chemical and physical properties.

    • Chemical Property: Characteristic that can change the chemical nature of a substance.

    • Example: burning.

    • Physical Property: Characteristic observed without changing the substance.

    • Examples include length, color, mass, and volume.

Metals, Nonmetals, and Metalloids

  • Metals:

    • Properties: Lustrous, malleable, good conductors of heat and electricity.

  • Nonmetals:

    • Definition: Elements that do not exhibit properties of metals.

  • Metalloids:

    • Definition: Elements that share some properties of metals but not all.

Grouped Elements

  • Group 1 (Alkali Metals excluding Hydrogen):

    • Very reactive, soft, with low melting and boiling points.

    • React with halogens to form halides and with nitrogen to form nitrides.

  • Group 2 (Alkaline Earth Metals):

    • Highly reactive with high melting and boiling points.

    • React vigorously with oxygen to form oxides and hydroxides; form alkaline solutions when dissolved in water.

  • Groups 3-12 (Transition Metals):

    • Less reactive, harder metals that can form more than one positive ion; good conductors of heat and electricity; high density; generally insoluble in water.

  • Halogens (Group 17 - Nonmetals):

    • Very reactive, diatomic elements that can exist in all states of matter at room temperature; extremely toxic; low melting and boiling points; brittle when solid.

  • Noble Gases (Group 18):

    • Very low reactivity, gases at room temperature with low melting and boiling points; generally insoluble in water.

  • Lanthanides:

    • Elements 57 to 71, known as rare earth metals, found in small quantities.

Characteristics of Families

  • Match the family with its most important characteristics:

    • Alkali Metal: Most reactive metal.

    • Alkaline Earth Metal: 2nd most reactive metal.

    • Transition Metals: Common metal, high melting point.

    • Halogen Family: Most reactive nonmetal.

    • Noble Gases: Do not react.

Chart of Atomic Particles

Charge

Particle

Location

Positive

Proton

Inside nucleus

Negative

Electron

Outside nucleus

Neutral

Neutron

Inside nucleus

Properties of Substances

  • Malleable: A substance can be hammered into sheets.

  • Ductile: A substance can be stretched into wires.

  • Luster: How light reflects off a substance.

  • Brittle: Easily broken into pieces.

  • Conductor: A substance that can carry electricity or heat.

Valence Electrons

  • Definition: The number of electrons in the outer shell of an atom.

  • Grouped by: Valence electrons, which are the electrons involved in chemical reactions.

  • Valency: The number of electrons an atom is willing to lose, gain, or share in a chemical reaction.

  • Group Number and Valence Electrons:

    • Group 1: 1 valence electron (Charge: +1)

    • Group 2: 2 valence electrons (Charge: +2)

    • Groups 13-16: Varies depending on group and element.

    • Group 15: Typically has 3 valence electrons (Charge: -3)

    • Group 14: Typically has 4 valence electrons (Charge: varies)

    • Group 17: Typically has 7 valence electrons (Charge: -1)

    • Group 18: Full valence shell (Charge: 0)

Chemical Bonds

  • Types of Chemical Bonds:

    • Ionic Bonds: Formed when atoms transfer electrons to achieve full valence shells, leading to positively and negatively charged ions.

    • Covalent Bonds: Formed when atoms share electrons to achieve stability in their outer electron shells.

When two atoms are chemically combined, it occurs in a fixed ratio.

Summary

  • A comprehensive understanding of atoms and the periodic table is crucial to grasping the fundamentals of chemistry. Each element has specific properties that influence its interactions and reactivity in various chemical reactions.