Ions and ionic bonds Revision Notes

Atoms are electrically neutral because they contain equal numbers of protons (positive charge) and electrons (negative charge). An ion is an atom or group of atoms that has gained or lost electrons, resulting in an overall electric charge. This charge can be positive or negative depending on whether electrons are lost or gained.

• Ions carry an electric charge due to unequal numbers of protons and electrons.
• Formation of ions involves electron transfer, not changes in protons.

When an atom loses one or more electrons, it has more protons than electrons, resulting in a net positive charge. Such positively charged ions are called cations. Metals tend to lose electrons to achieve a stable electron arrangement, often resembling the nearest noble gas configuration.

For example, a sodium atom (Na) has 11 electrons. By losing one electron, it forms a sodium ion (Na⁺) with 10 electrons and 11 protons, giving it a +1 charge.

• Cations form by losing electrons.
• Metals commonly form cations.
• Example: Na → Na⁺ + e⁻

When an atom gains one or more electrons, it has more electrons than protons, resulting in a net negative charge. These negatively charged ions are called anions. Non-metal atoms tend to gain electrons to complete their outer electron shell, achieving a stable electron configuration.

For example, a chlorine atom (Cl) has 17 electrons. By gaining one electron, it forms a chloride ion (Cl⁻) with 18 electrons and 17 protons, giving it a -1 charge.

• Anions form by gaining electrons.
• Non-metals commonly form anions.
• Example: Cl + e⁻ → Cl⁻

The formation of cations and anions is fundamental to ionic bonding. When a metal atom loses electrons to become a cation and a non-metal atom gains those electrons to become an anion, the opposite charges attract each other. This electrostatic attraction forms a strong ionic bond, creating ionic compounds such as sodium chloride (NaCl).

This electron transfer explains the charged nature of ions and the resulting ionic lattice structures in compounds.

• Electron transfer creates charged ions.
• Opposite charges attract, forming ionic bonds.
• Example: Na⁺ and Cl⁻ combine to form NaCl.

In summary, ions form by atoms gaining or losing electrons to achieve stable electron configurations. Metals lose electrons to form cations, while non-metals gain electrons to form anions. This process is essential for the formation of ionic compounds and understanding chemical reactions involving ions.

• Ions result from electron gain or loss.
• Cations = positive ions (electron loss).
• Anions = negative ions (electron gain).
• Ionic compounds consist of cations and anions held by ionic bonds.

Atoms can become ions by gaining or losing electrons. Metals tend to lose electrons to form positively charged ions called cations, while non-metals tend to gain electrons to form negatively charged ions called anions.

For example, a sodium atom (Na) loses one electron to become a Na⁺ ion, and a chlorine atom (Cl) gains one electron to become a Cl⁻ ion. This transfer of electrons results in ions with opposite charges.

The loss or gain of electrons changes the balance between protons and electrons in the atom, creating charged particles (ions).

• Metals lose electrons → form cations (+ charge).
• Non-metals gain electrons → form anions (− charge).
• Electron transfer leads to charged ions.

Once ions with opposite charges are formed, they attract each other due to electrostatic forces. These forces are the attraction between positive and negative charges, similar to how opposite poles of magnets attract.

This attraction is non-directional and acts in all directions, pulling the ions together to form a stable ionic bond.

The strength of this electrostatic attraction depends on the magnitude of the charges and the distance between the ions. Higher charges and smaller distances result in stronger attractions.

• Opposite charges attract via electrostatic forces.
• Attraction is strong and acts in all directions.
• Strength depends on charge magnitude and ion size.

An ionic bond is the strong force holding ions together in an ionic compound. It is much stronger than many other types of intermolecular forces because it involves full positive and negative charges.

This strong attraction gives ionic compounds distinctive properties such as high melting and boiling points, as a lot of energy is needed to overcome the ionic bonds.

For example, sodium chloride (NaCl) consists of Na⁺ and Cl⁻ ions held together by strong ionic bonds formed by electrostatic attraction.

• Ionic bonds are strong due to full charges.
• Strong bonds lead to high melting/boiling points.
• Example: NaCl held by ionic bonds.

Sodium (Na), a metal, has one electron in its outer shell. Chlorine (Cl), a non-metal, has seven electrons in its outer shell.

Sodium transfers its one outer electron to chlorine. Sodium becomes Na⁺, chlorine becomes Cl⁻.

The Na⁺ and Cl⁻ ions attract each other strongly by electrostatic forces, forming the ionic bond in sodium chloride (NaCl).

• Na loses 1 electron → Na⁺.
• Cl gains 1 electron → Cl⁻.
• Na⁺ and Cl⁻ attract strongly → ionic bond.

Ionic bonds form when atoms transfer electrons to become ions with opposite charges.

The electrostatic attraction between these oppositely charged ions is the ionic bond.

This bond is strong because it involves full positive and negative charges attracting each other over short distances, creating stable ionic compounds.

• Electron transfer creates ions.
• Opposite charges attract strongly.
• Ionic bonds are strong electrostatic forces.

Group I elements, such as sodium (Na), have one electron in their outermost shell. They tend to lose this electron to achieve a stable electron configuration similar to the nearest noble gas.

Group VII elements, such as chlorine (Cl), have seven electrons in their outer shell and need one more electron to complete their octet and become stable.

When a Group I atom reacts with a Group VII atom, the Group I atom transfers its outer electron to the Group VII atom. This electron transfer results in the formation of ions: the Group I atom becomes a positively charged ion (cation), and the Group VII atom becomes a negatively charged ion (anion).

• Group I atom loses 1 electron → forms cation (e.g., Na → Na⁺).
• Group VII atom gains 1 electron → forms anion (e.g., Cl → Cl⁻).

The oppositely charged ions (cations and anions) attract each other due to electrostatic forces. This attraction is the ionic bond, which holds the ions together in an ionic compound.

Ionic bonds are strong because the electrostatic forces act in all directions between the ions, creating a stable structure.

For example, sodium chloride (NaCl) forms when Na⁺ and Cl⁻ ions attract each other to form a giant ionic lattice.

• Ionic bond = electrostatic attraction between oppositely charged ions.
• Example: Na⁺ + Cl⁻ → NaCl (ionic compound).

Dot-and-cross diagrams visually show the transfer of electrons from one atom to another during ionic bonding.

In these diagrams, electrons from one atom are represented by dots, and electrons from the other atom by crosses, making it clear which electrons come from which atom.

For sodium and chlorine, the sodium atom’s single outer electron (dot) is transferred to chlorine’s outer shell (crosses), completing chlorine’s octet and emptying sodium’s outer shell.

• Dots represent electrons from one element; crosses represent electrons from the other.
• Transferred electrons appear in the outer shell of the receiving atom.
• The resulting ions have full outer shells, shown by completed octets in the diagram.

Sodium (Na) has one electron in its outer shell; chlorine (Cl) has seven electrons in its outer shell.

Sodium loses its one outer electron to form Na⁺, achieving the electron configuration of neon.

Chlorine gains one electron to form Cl⁻, achieving the electron configuration of argon, a noble gas with a full outer shell of eight electrons (octet).

• Na → Na⁺ + e⁻
• Cl + e⁻ → Cl⁻
• Na⁺ and Cl⁻ attract to form NaCl.

Group I atoms lose electrons to form cations with a full outer shell.

Group VII atoms gain electrons to form anions with a full outer shell.

The electrostatic attraction between these ions forms a strong ionic bond, creating ionic compounds with characteristic properties.

• Electron transfer leads to ion formation.
• Opposite charges attract, forming ionic bonds.
• Dot-and-cross diagrams clearly illustrate electron transfer and ion formation.

Ionic compounds consist of positive and negative ions arranged in a giant lattice structure. The ions are held together by strong electrostatic forces of attraction between oppositely charged ions, known as ionic bonds.

These forces require a large amount of energy to overcome, which results in ionic compounds having high melting and boiling points compared to covalent compounds.

For example, sodium chloride (NaCl) melts at about 801 °C and boils at 1413 °C, reflecting the strength of the ionic bonds in its lattice.

• Ionic bonds are strong electrostatic attractions between oppositely charged ions.
• High melting and boiling points indicate strong ionic bonding.
• Energy input must be sufficient to break many ionic bonds in the lattice.

In solid ionic compounds, ions are fixed in place within the lattice and cannot move freely, so they do not conduct electricity.

When an ionic compound is melted or dissolved in water, the lattice breaks down, freeing the ions to move.

These free ions act as charge carriers, allowing the substance to conduct electricity in molten or aqueous states.

• Solid ionic compounds do not conduct electricity due to immobile ions.
• Molten or aqueous ionic compounds conduct electricity because ions are free to move.
• This property distinguishes ionic compounds from covalent compounds, which generally do not conduct electricity in any state.

Water is a polar solvent, meaning it has partial positive and negative charges on different parts of its molecules.

Ionic compounds tend to dissolve in water because the polar water molecules surround and separate the positive and negative ions, a process called hydration.

This breaks the ionic lattice apart, allowing the ions to disperse evenly in solution, forming an electrolyte solution that conducts electricity.

• Water molecules interact with ions, overcoming ionic bonds in the lattice.
• Most ionic compounds are soluble in water due to this interaction.
• Solubility varies depending on the specific ionic compound and lattice energy.

Sodium chloride (NaCl) is a classic ionic compound with high melting and boiling points, conducts electricity when molten or dissolved, and is soluble in water.

Magnesium oxide (MgO) has even higher melting and boiling points due to the +2 and -2 charges on its ions, increasing electrostatic attraction.

Copper(II) sulfate (CuSO4) dissolves in water and conducts electricity in solution, demonstrating typical ionic behaviour.

• NaCl melts at 801 °C and conducts electricity when molten.
• MgO has a melting point above 2800 °C due to stronger ionic bonds.
• CuSO4 dissolves in water forming a conductive solution.

The strong ionic bonds in ionic compounds result in high melting and boiling points.

Electrical conductivity depends on the mobility of ions: solid ionic compounds do not conduct, but molten or aqueous forms do.

Most ionic compounds dissolve in water because water molecules separate the ions, allowing them to disperse and conduct electricity.

• High melting/boiling points due to strong ionic bonds.
• Conduct electricity only when ions are free to move (molten or aqueous).
• Generally soluble in water due to hydration of ions.

Ionic bonding occurs when a metal atom transfers one or more electrons to a non-metal atom. Metals have relatively few electrons in their outer shell and tend to lose these electrons to achieve a stable electron arrangement, often resembling the nearest noble gas configuration. When a metal atom loses electrons, it becomes a positively charged ion, called a cation.

Non-metal atoms have more electrons in their outer shell and tend to gain electrons to complete their outer shell. When a non-metal atom gains electrons, it becomes a negatively charged ion, called an anion.

This transfer of electrons results in the formation of ions with opposite charges, which are strongly attracted to each other by electrostatic forces, creating an ionic bond.

• Metals lose electrons → form positive ions (cations).
• Non-metals gain electrons → form negative ions (anions).
• Oppositely charged ions attract → ionic bond formed.

Dot-and-cross diagrams are a useful way to show the transfer of electrons during ionic bond formation. In these diagrams, electrons from one atom are represented by dots, and electrons from the other atom are represented by crosses. This distinction helps visualise which electrons come from which atom.

The diagram shows the outer electrons of the metal atom being removed (dots or crosses) and added to the outer shell of the non-metal atom, completing its outer shell.

After the transfer, the metal ion is shown with a full positive charge and the non-metal ion with a full negative charge, illustrating the formation of ions and the ionic bond between them.

• Dots and crosses represent electrons from different atoms.
• Electron transfer is shown by moving dots or crosses from metal to non-metal.
• Resulting ions have full outer shells and opposite charges.

Sodium (Na) is a metal with one electron in its outer shell. Chlorine (Cl) is a non-metal with seven electrons in its outer shell.

Sodium transfers its one outer electron to chlorine. Sodium becomes Na⁺ (a cation) with a full outer shell, and chlorine becomes Cl⁻ (an anion) with a full outer shell.

The electrostatic attraction between Na⁺ and Cl⁻ forms the ionic bond, creating sodium chloride (NaCl). The dot-and-cross diagram shows sodium’s electron (dot) moving to chlorine’s outer shell (crosses), completing chlorine’s octet.

• Na loses 1 electron → Na⁺ ion.
• Cl gains 1 electron → Cl⁻ ion.
• Na⁺ and Cl⁻ attract to form NaCl ionic bond.

Ionic bonds are strong due to the electrostatic attraction between oppositely charged ions. This strength leads to high melting and boiling points in ionic compounds.

The transfer of electrons means ionic compounds consist of charged particles arranged in a giant lattice structure, which is stable and rigid.

Understanding electron transfer and ionic bond formation helps explain the properties of ionic compounds, such as electrical conductivity when molten or dissolved in water, but not in solid form.

• Strong electrostatic forces → strong ionic bonds.
• Ionic compounds form giant ionic lattices.
• Properties relate to ionic bonding and structure.

When drawing dot-and-cross diagrams for ionic bonding, clearly show the outer electrons of each atom before and after electron transfer.

Use different symbols (dots and crosses) to represent electrons from each atom to avoid confusion.

Label the resulting ions with their charges and show the full outer shells after electron transfer to demonstrate understanding of ionic bond formation.

• Show initial outer electrons of metal and non-metal.
• Indicate electron transfer with arrows or movement of dots/crosses.
• Label ions with correct charges and full outer shells.

Ionic compounds are formed when atoms transfer electrons to achieve stable electron configurations, resulting in positively charged ions (cations) and negatively charged ions (anions). For example, sodium (Na) loses one electron to become Na⁺, while chlorine (Cl) gains one electron to become Cl⁻. These oppositely charged ions attract each other due to electrostatic forces, forming ionic bonds.

• Sodium loses one electron → Na⁺ (cation)
• Chlorine gains one electron → Cl⁻ (anion)
• Opposite charges attract, forming ionic bonds

Unlike simple molecules, ionic compounds do not exist as discrete units but form a giant lattice structure. This structure is a three-dimensional, repeating pattern of alternating positive and negative ions. Each ion is surrounded by ions of opposite charge, maximising attraction and minimising repulsion, which stabilises the structure.

In sodium chloride, each Na⁺ ion is surrounded by six Cl⁻ ions, and each Cl⁻ ion is surrounded by six Na⁺ ions. This arrangement is called a cubic lattice and extends in all directions, creating a rigid and stable solid.

• Ions arranged in a regular, repeating 3D pattern
• Each ion surrounded by oppositely charged ions
• Sodium chloride forms a cubic lattice with coordination number 6

The lattice is held together by strong electrostatic forces of attraction between the oppositely charged ions. These forces act in all directions, making the lattice very stable and giving ionic compounds high melting and boiling points.

The strength of these forces depends on the charge of the ions and the distance between them. In sodium chloride, the single positive and negative charges and relatively small ionic radii result in strong attractions.

• Strong electrostatic attraction between Na⁺ and Cl⁻ ions
• Forces act in all directions in the lattice
• High melting and boiling points result from strong ionic bonds

The giant lattice structure explains many physical properties of ionic compounds. The strong ionic bonds require a lot of energy to break, so ionic compounds like sodium chloride have high melting and boiling points.

In solid form, the ions are fixed in place and cannot conduct electricity. However, when melted or dissolved in water, the ions are free to move, allowing the compound to conduct electricity.

The regular arrangement also contributes to the brittleness of ionic solids; applying force can shift ions so that like charges align and repel, causing the lattice to break.

• High melting and boiling points due to strong ionic bonds
• Conduct electricity when molten or dissolved, not when solid
• Brittle due to repulsion when lattice layers shift