Chemistry 1

An atom is the basic unit of a chemical element, consisting of a central nucleus surrounded by a cloud of negatively charged electrons.

1. Subatomic Particles

The core structure of an atom is defined by three fundamental subatomic particles:

• Protons

  • Located within the nucleus.

  • Possess a relative charge of $+1$.

  • Have a relative mass of $1\,\text{amu}$.

  • Determine the atomic number ($Z$) and identity of the element.

• Neutrons

  • Located within the nucleus.

  • Carry a neutral charge ($0$).

  • Have a relative mass of $1\,\text{amu}$.

  • Contribute to the nuclear stability and mass number ($A$).

• Electrons

  • Orbit the nucleus in specific energy levels or orbitals.

  • Possess a relative charge of $-1$.

  • Have a negligible relative mass (approximately $\frac{1}{1836}\,\text{amu}$).

2. Atomic Numbers and Notation

• Atomic Number ($Z$)

  • Represents the total number of protons in the nucleus of an atom.

  • In a neutral atom, the number of protons equals the number of electrons.

• Mass Number ($A$)

  • The total number of protons and neutrons in the nucleus:
    $\text{Mass Number }(A) = \text{Protons }(Z) + \text{Neutrons }(N)$

• Isotopes

  • Atoms of the same element with the same atomic number ($Z$) but different mass numbers ($A$) due to varying numbers of neutrons.

3. Electronic Structure

• Energy Levels (Shells)

  • Electrons occupy principal energy levels designated by the principal quantum number $n$ ($n = 1, 2, 3, \dots$).

  • The maximum number of electrons that a shell can hold is given by the formula $2n^2$.

• Subshells and Orbitals

  • Energy levels are divided into subshells: $s$, $p$, $d$, and $f$.

  • An orbital can hold a maximum of $2$ electrons with opposite spins.

An atom is the basic unit of a chemical element, consisting of a central nucleus surrounded by a cloud of negatively charged electrons.

1. Subatomic Particles

The core structure of an atom is defined by three fundamental subatomic particles:

• Protons

  • Located within the nucleus.

  • Possess a relative charge of $+1$.

  • Have a relative mass of $1\,\text{amu}$.

  • Determine the atomic number ($Z$) and identity of the element.

• Neutrons

  • Located within the nucleus.

  • Carry a neutral charge ($0$).

  • Have a relative mass of $1\,\text{amu}$.

  • Contribute to the nuclear stability and mass number ($A$).

• Electrons

  • Orbit the nucleus in specific energy levels or orbitals.

  • Possess a relative charge of $-1$.

  • Have a negligible relative mass (approximately $\frac{1}{1836}\,\text{amu}$).

2. Atomic Numbers and Notation

• Atomic Number ($Z$)

  • Represents the total number of protons in the nucleus of an atom.

  • In a neutral atom, the number of protons equals the number of electrons.

• Mass Number ($A$)

  • The total number of protons and neutrons in the nucleus:
    $\text{Mass Number }(A) = \text{Protons }(Z) + \text{Neutrons }(N)$

• Isotopes

  • Atoms of the same element with the same atomic number ($Z$) but different mass numbers ($A$) due to varying numbers of neutrons.

3. Electronic Structure

• Energy Levels (Shells)

  • Electrons occupy principal energy levels designated by the principal quantum number $n$ ($n = 1, 2, 3, \dots$).

  • The maximum number of electrons that a shell can hold is given by the formula $2n^2$.

• Subshells and Orbitals

  • Energy levels are divided into subshells: $s$, $p$, $d$, and $f$.

  • An orbital can hold a maximum of $2$ electrons with opposite spins.

4. Chemical Bonding

• Ionic Bonding

  • Strong electrostatic attraction between oppositely charged ions formed by electron transfer.

  • Typically occurs between metals and non-metals.

• Covalent Bonding

  • Electrostatic attraction between shared pairs of electrons and the positively charged nuclei.

  • Typically occurs between non-metal atoms.

• Metallic Bonding

  • Electrostatic attraction between positive metal ions and a sea of delocalized electrons.