Chemical Changes and Structure ( section 1 )

What are the three sub-atomic particles found in an atom, and what are their charges?

• Protons: Positive charge (+$1)
• Neutrons: No charge (0)
• Electrons: Negative charge ($-$1)

What is the atomic number (Z) of an element, and what does it tell us?

The atomic number (Z) is the number of protons in the nucleus of an atom. It determines the identity of an element. In a neutral atom, it is also equal to the number of electrons.

What is the mass number (A) of an atom?

The mass number (A) is the total number of protons and neutrons in the nucleus of an atom.
A = \text{number of protons} + \text{number of neutrons}

Define isotopes.

Isotopes are atoms of the same element (same atomic number, Z) that have different numbers of neutrons, and therefore different mass numbers (A).
Example: Carbon-12 (6 protons, 6 neutrons) and Carbon-14 (6 protons, 8 neutrons).

What are the three sub-atomic particles found in an atom, and what are their charges?

• Protons: Positive charge (+$1)
• Neutrons: No charge (0)
• Electrons: Negative charge ($-$1)

What is the atomic number (Z) of an element, and what does it tell us?

The atomic number (Z) is the number of protons in the nucleus of an atom. It determines the identity of an element. In a neutral atom, it is also equal to the number of electrons.

What is the mass number (A) of an atom?

The mass number (A) is the total number of protons and neutrons in the nucleus of an atom.

A = \text{number of protons} + \text{number of neutrons}

Define isotopes.

Isotopes are atoms of the same element (same atomic number, Z) that have different numbers of neutrons, and therefore different mass numbers (A).

Example: Carbon-12 (6 protons, 6 neutrons) and Carbon-14 (6 protons, 8 neutrons).

What is Relative Atomic Mass (A_r)?

Relative Atomic Mass (A_r) is the weighted average mass of naturally occurring isotopes of an element compared to 1/12th the mass of a carbon-12 atom. It takes into account the abundance of each isotope.

What is a mole, and what is Avogadro's Constant?

• A mole is the amount of substance that contains as many elementary entities (atoms, molecules, ions, etc.) as there are atoms in exactly 12 grams of carbon-12.
• Avogadro's Constant (L or N_A) is the number of entities in one mole, approximately 6.02 \times 10^{23} \text{mol}^{-1}.

How is molar mass (M) defined, and what are its standard units?

Molar mass (M) is the mass of one mole of a substance. Its standard units are grams per mole (\text{g mol}^{-1}).
For an element, its molar mass in \text{g mol}^{-1} is numerically equal to its relative atomic mass.
For a compound, its molar mass is the sum of the relative atomic masses of all atoms in its chemical formula.

Briefly describe ionic bonding.

Ionic bonding occurs between a metal and a non-metal, involving the transfer of electrons from the metal atom to the non-metal atom, forming oppositely charged ions which are then attracted to each other by electrostatic forces.

Briefly describe covalent bonding.

Covalent bonding occurs between two non-metal atoms, involving the sharing of one or more pairs of electrons between the atoms to achieve a stable outer electron shell.

What is electronegativity?

Electronegativity is a measure of the attraction an atom has for the bonding electrons in a covalent bond.

Describe the trends in electronegativity across the periodic table.

Trends in electronegativity:

• It increases across a period (left to right) due to increasing nuclear charge and decreasing atomic radius.
• It decreases down a group (top to bottom) due to increasing atomic radius and shielding by inner electrons.

What is a polar covalent bond?

Unequal sharing of electrons in a covalent bond, resulting in one end of the bond being slightly positive (\delta+) and the other slightly negative (\delta-). This occurs when there is a significant difference in electronegativity between the two bonded atoms.

What is a non-polar covalent bond?

Equal sharing of electrons in a covalent bond, occurring when the two bonded atoms have similar or identical electronegativities (e.g., H2, Cl2).

What are Intermolecular Forces (IMFs)?

forces of attraction between molecules (intermolecular forces are weaker than intramolecular bonds like covalent or ionic bonds).

Describe discrete molecular covalent structures and their properties.

Involve individual molecules held together by weak intermolecular forces. Substances with this structure typically have low melting and boiling points, are usually gases or liquids at room temperature, and are poor conductors of electricity (e.g., \text{H}2\text{O}, CO2).

Describe giant covalent network structures and their properties, providing examples.

Involve a vast network of atoms held together by strong covalent bonds throughout the entire structure. These substances typically have very high melting and boiling points, are hard, and are generally poor conductors of electricity (e.g., diamond, silicon dioxide).

What is metallic bonding?

Metallic bonding is the electrostatic attraction between positively charged metal ions and a 'sea' of delocalised electrons. These electrons are not associated with any single atom or bond but are free to move throughout the structure.

What are the general properties of substances with metallic bonding?

Metals are typically good conductors of electricity and heat, malleable, and ductile due to the mobility of their delocalised electrons.

What are the three sub-atomic particles found in an atom, and what are their charges?

• Protons: Positive charge (+$1)
• Neutrons: No charge (0)
• Electrons: Negative charge ($-$1)

What is the atomic number (Z) of an element, and what does it tell us?

The atomic number (Z) is the number of protons in the nucleus of an atom. It determines the identity of an element. In a neutral atom, it is also equal to the number of electrons.

What is the mass number (A) of an atom?

The mass number (A) is the total number of protons and neutrons in the nucleus of an atom.

A = \text{number of protons} + \text{number of neutrons}

Define isotopes.

Isotopes are atoms of the same element (same atomic number, Z) that have different numbers of neutrons, and therefore different mass numbers (A).

Example: Carbon-12 (6 protons, 6 neutrons) and Carbon-14 (6 protons, 8 neutrons).

What are the three sub-atomic particles found in an atom, and what are their charges?

• Protons: Positive charge (+$1)
• Neutrons: No charge (0)
• Electrons: Negative charge ($-$1)

What is the atomic number (Z) of an element, and what does it tell us?

The atomic number (Z) is the number of protons in the nucleus of an atom. It determines the identity of an element. In a neutral atom, it is also equal to the number of electrons.

What is the mass number (A) of an atom?

The mass number (A) is the total number of protons and neutrons in the nucleus of an atom.

A = \text{number of protons} + \text{number of neutrons}

Define isotopes.

Isotopes are atoms of the same element (same atomic number, Z) that have different numbers of neutrons, and therefore different mass numbers (A).

Example: Carbon-12 (6 protons, 6 neutrons) and Carbon-14 (6 protons, 8 neutrons).

What is Relative Atomic Mass (A_r)?

Relative Atomic Mass (A_r) is the weighted average mass of naturally occurring isotopes of an element compared to 1/12th the mass of a carbon-12 atom. It takes into account the abundance of each isotope.

What is a mole, and what is Avogadro's Constant?

• A mole is the amount of substance that contains as many elementary entities (atoms, molecules, ions, etc.) as there are atoms in exactly 12 grams of carbon-12.
• Avogadro's Constant (L or N_A) is the number of entities in one mole, approximately 6.02 \times 10^{23} \text{mol}^{-1}.

How is molar mass (M) defined, and what are its standard units?

Molar mass (M) is the mass of one mole of a substance. Its standard units are grams per mole (\text{g mol}^{-1}).

For an element, its molar mass in \text{g mol}^{-1} is numerically equal to its relative atomic mass.

For a compound, its molar mass is the sum of the relative atomic masses of all atoms in its chemical formula.

Briefly describe ionic bonding.

Ionic bonding occurs between a metal and a non-metal, involving the transfer of electrons from the metal atom to the non-metal atom, forming oppositely charged ions which are then attracted to each other by electrostatic forces.

Briefly describe covalent bonding.

Covalent bonding occurs between two non-metal atoms, involving the sharing of one or more pairs of electrons between the atoms to achieve a stable outer electron shell.

What is electronegativity?

Electronegativity is a measure of the attraction an atom has for the bonding electrons in a covalent bond.

Describe the trends in electronegativity across the periodic table.

Trends in electronegativity:

• It increases across a period (left to right) due to increasing nuclear charge and decreasing atomic radius.
• It decreases down a group (top to bottom) due to increasing atomic radius and shielding by inner electrons.

What is a polar covalent bond?

Unequal sharing of electrons in a covalent bond, resulting in one end of the bond being slightly positive (\delta+) and the other slightly negative (\delta-). This occurs when there is a significant difference in electronegativity between the two bonded atoms.

What is a non-polar covalent bond?

Equal sharing of electrons in a covalent bond, occurring when the two bonded atoms have similar or identical electronegativities (e.g., H2, Cl2).

What are Intermolecular Forces (IMFs)?

forces of attraction between molecules (intermolecular forces are weaker than intramolecular bonds like covalent or ionic bonds).

Describe discrete molecular covalent structures and their properties.

Involve individual molecules held together by weak intermolecular forces. Substances with this structure typically have low melting and boiling points, are usually gases or liquids at room temperature, and are poor conductors of electricity (e.g., \text{H}2\text{O}, CO2).

Describe giant covalent network structures and their properties, providing examples.

Involve a vast network of atoms held together by strong covalent bonds throughout the entire structure. These substances typically have very high melting and boiling points, are hard, and are generally poor conductors of electricity (e.g., diamond, silicon dioxide).

What is metallic bonding?

Metallic bonding is the electrostatic attraction between positively charged metal ions and a 'sea' of delocalised electrons. These electrons are not associated with any single atom or bond but are free to move throughout the structure.

Metals are typically good conductors of electricity and heat, malleable, and ductile