Bonding (Edexcel A Level Chemistry): Flashcards

True.

Calcium is a Group 2 metal and loses both of its outer electrons to form a Ca²⁺ ion, achieving the electronic configuration of argon.

When drawing a dot-and-cross diagram for an ionic compound: only outer-shell electrons are shown; brackets are drawn around each ion to indicate the charge is spread evenly; and the charge on each ion is written at the top right-hand corner of the bracket.

In calcium fluoride (CaF₂), each Ca²⁺ ion bonds with two F^- ions because each fluorine atom can only accept one electron.

In lithium nitride, nitrogen gains 3 electrons to form an N^3- ion. Each lithium atom can only donate one electron, so three Li⁺ ions are needed to supply the 3 electrons required to cancel out the 3- charge.

In aluminium oxide (Al₂O₃), aluminium forms an Al³⁺ ion by losing 3 electrons and oxygen forms an O^2- ion by gaining 2 electrons.

True.

In any ionic compound, the total positive charge of the cations exactly cancels out the total negative charge of the anions, making the overall compound electrically neutral.

In aluminium oxide, 2 Al³⁺ ions (total charge 6+) and 3 O^2- ions (total charge 6-) are needed, giving the formula Al₂O₃ with an overall neutral charge.

The bracket in a dot-and-cross diagram indicates that the ion has an overall charge, with that charge spread evenly across the ion. The charge value is written at the top right-hand corner of the bracket.

Ionic radius is a measure of the size of an ion, reflecting the distance from the nucleus to the outermost electron shell of that ion.

Ionic radius increases as negative charge increases. Gaining electrons pushes the outermost electrons further from the nucleus and reduces the effective nuclear attraction per electron, making the ion larger.

True.

Mg²⁺ has more protons (12) than Na⁺ (11) but the same number of electrons [2,8]. The greater nuclear charge in Mg²⁺ pulls the electrons closer to the nucleus, giving a smaller ionic radius.

As positive charge increases, ionic radius decreases because the same nuclear charge attracts fewer electrons more strongly.

Isoelectronic ions are ions that have the same number of electrons (and therefore the same electronic configuration) but different numbers of protons.

For isoelectronic ions, the number of protons determines ionic radius. As the number of protons increases, the nuclear charge pulls the fixed number of electrons closer to the nucleus, so ionic radius decreases across the series.

True.

N^3- has only 7 protons while Al³⁺ has 13, yet both have 10 electrons. The weaker nuclear attraction in N^3- means its electrons are held less tightly, giving it a larger ionic radius (0.171 nm vs 0.054 nm).

N^3-, O^2-, F^-, Na⁺, Mg²⁺ and Al³⁺ are all isoelectronic ions because they all have the electronic configuration 1s² 2s² 2p⁶.

A negative ion has a larger radius than its parent atom because gaining electrons increases the number of electrons repelling each other. The nuclear charge remains the same, so each electron is held less tightly and the electron cloud expands.

A giant ionic lattice is a three-dimensional, regularly repeating arrangement of alternating positive and negative ions held together by strong electrostatic forces of attraction in all directions.

Ionic compounds have high melting points because the electrostatic forces of attraction between oppositely charged ions in the giant lattice are very strong, requiring a large amount of energy to overcome.

False.

In the solid state, ions are held in fixed positions within the lattice and cannot move. Electrical conductivity requires freely moving charged particles, so solid ionic compounds do not conduct.

Ionic compounds conduct electricity when molten or dissolved in solution because the ions are free to move and carry charge.

A greater ionic charge increases the strength of the electrostatic attraction between cations and anions. Stronger forces require more energy to overcome, so the melting point is higher. For example, CaO (2845 K) has a much higher melting point than Na₂O (1405 K).

False.

CaO (2845 K) has a much higher melting point than NaCl because Ca²⁺ and O^2- carry greater ionic charges than Na⁺ and Cl^-, producing stronger electrostatic forces of attraction in the lattice.

Many ionic compounds dissolve in polar solvents such as water because the polar molecules can break down the ionic lattice and surround each ion.

Polar water molecules orientate so that the δ+ end surrounds the anions and the δ- end surrounds the cations. This disrupts the ionic lattice, and the ions become surrounded (hydrated) by water molecules and disperse into solution.

During electrolysis of copper(II) chromate(VI), the blue Cu²⁺ ions migrate to the negative electrode and the yellow CrO₄^2- ions migrate to the positive electrode. The visible separation of colours confirms that the substance contains distinct, independently moving charged ions.

True.

Ions with a greater ionic charge form stronger electrostatic attractions within the lattice, making it harder for water molecules to disrupt the structure and dissolve the compound.

A covalent bond is an electrostatic attraction between the nuclei of two atoms and their shared bonding electrons. It forms between two non-metal atoms and involves no transfer of electrons.

False.

In a covalent bond, electrons are shared between the two atoms. No electrons are transferred.

The electrostatic attraction in a covalent bond is between the nuclei of the two bonded atoms and the shared bonding electrons in their outer shells.

Covalent bonding occurs between two non-metal atoms.

Sharing electrons allows each atom to achieve an electron configuration similar to that of a noble gas, which is a lower energy and more stable arrangement.

False.

Covalent bonding occurs only between non-metal atoms. Bonding between a metal and a non-metal is typically ionic.

A single covalent bond is a covalent bond formed by the sharing of one pair of electrons between two atoms.

In a covalent bond, each atom achieves an electron configuration similar to a noble gas by sharing electrons.

Non-metal elements form covalent bonds with each other. They share pairs of electrons from their outer shells to achieve a more stable electron configuration.

A dative covalent bond is a covalent bond in which both electrons are donated by the same atom. It is also called coordinate bonding.

True.

In a dative covalent bond, one atom donates a lone pair of electrons to an electron-deficient atom. Both electrons therefore originate from the same atom.

An electron-deficient atom is one that has an unfilled outer orbital and therefore has space to accept a pair of electrons from another atom.

In dative covalent bonding, both electrons in the shared pair are donated by the same atom, which must have a lone pair available.

The nitrogen atom in ammonia has a lone pair of electrons. It donates this lone pair to the electron-deficient H⁺ ion, which has an empty outer shell, forming a dative covalent bond and producing the ammonium ion NH₄⁺.

False.

At lower temperatures, two AlCl₃ molecules combine to form a dimer (Al₂Cl₆) via dative covalent bonds. At high temperatures it exists as a monomer.

Two AlCl₃ molecules join when lone pairs on two chlorine atoms form dative covalent bonds with the electron-deficient aluminium atoms of each molecule, producing the dimer Al₂Cl₆.

In a dot-and-cross diagram, atoms in covalent compounds share their outer valence electrons to achieve a noble gas configuration.

Dot-and-cross diagrams show the outer shell electrons of each atom using dots or crosses. Shared pairs in the covalent bond region are shown between the two atoms, illustrating which atom each electron originated from.

Bond energy is the energy required to break one mole of a particular covalent bond in the gaseous state. It is measured in kJ mol^-1.

True.

Triple bonds have greater electron density between the nuclei, increasing the forces of attraction and pulling the atoms closer together. This gives a shorter bond length and greater bond strength.

Bond length is the internuclear distance between two covalently bonded atoms. It is the distance from the nucleus of one atom to the nucleus of the other atom forming the bond.

Triple bonds have the largest electron density between the nuclei of the two bonded atoms. This creates greater forces of attraction between the electrons and the nuclei, pulling the atoms closer together and resulting in the shortest bond length.

The larger the bond energy, the stronger the covalent bond.

Bond length and bond strength are inversely related: as bond length decreases, bond strength increases. A shorter bond has greater forces of attraction between the nuclei and bonding electrons, making it harder to break.

False.

Increasing the electron density between two nuclei strengthens the covalent bond. The greater forces of attraction pull the atoms closer, decreasing the bond length and increasing bond strength.

Bond energy is the energy required to break one mole of a covalent bond in the gaseous state and has units of kJ mol^-1 .

As the forces of attraction between electrons and nuclei increase, bond length decreases. The atoms are pulled closer together, resulting in a shorter and stronger covalent bond.

VSEPR theory (valence shell electron pair repulsion theory) predicts the shape and bond angles of molecules based on the principle that electron pairs around a central atom repel each other and adopt positions that minimise this repulsion.

True.

Lone pairs have a more concentrated electron charge cloud that is closer to the central nucleus. This gives them greater repulsive force than bonding pairs, which are shared between two nuclei and spread out more.

A molecule with 4 bonding pairs and no lone pairs adopts a tetrahedral shape with a bond angle of 109.5°.

In VSEPR theory, the most stable shape is the one that minimises the repulsion between electron pairs around the central atom.

Lone pairs exert greater repulsion than bonding pairs, pushing the bonding pairs closer together. This reduces the bond angles compared to a molecule with the same number of bonding pairs but no lone pairs.

False.

A molecule with 3 bonding pairs and 1 lone pair has a trigonal pyramidal shape, not trigonal planar. The lone pair pushes the bonding pairs downward, giving a bond angle of approximately 107°.

In decreasing order of repulsion strength:

1. Lone pair – lone pair (greatest)

2. Lone pair – bond pair

3. Bond pair – bond pair (least)

Phosphorus pentachloride (PCl₅) has 5 bonding pairs and no lone pairs, giving it a trigonal bipyramidal shape.

A lone pair is a pair of electrons in the outer shell of an atom that is not involved in bonding. Lone pairs have a greater repulsive effect than bonding pairs because their charge cloud is more concentrated.

Lone pairs have a more concentrated electron charge cloud that is wider and positioned closer to the central atom's nucleus. This gives them a greater repulsive effect than bonding pairs, which are shared between two nuclei and are more spread out.