2.1 Bonding, Structure & Properties (WJEC GCSE Chemistry): Flashcards

In a metal, the outer electrons become delocalised and form a 'sea of electrons' surrounding the positive metal ions.

False.

Metals are malleable because the layers of positive ions can slide over each other when a force is applied. There are no covalent bonds in metallic structures.

A malleable material is one that can be hammered or pressed into shape without breaking. In metals, this is possible because layers of ions can slide over each other.

Most metals have high melting and boiling points because there are strong electrostatic forces of attraction between the positive metal ions and the delocalised electrons, which require a large amount of energy to overcome.

True.

As you go across a period, more electrons become delocalised. This increases the forces of attraction between the positive ions and the electron sea, requiring more energy to overcome and resulting in a higher melting point.

Metallic bonding occurs in metals and metal alloys, which are mixtures of metallic elements.

An ion is an electrically charged atom or group of atoms formed by the loss or gain of electrons.

A cation is a positively charged ion formed when an atom loses electrons, whereas an anion is a negatively charged ion formed when an atom gains electrons.

Metals lose electrons to form positive ions, while non-metals gain electrons to form negative ions.

True.

Atoms lose or gain electrons to achieve a full outer shell, giving them the same electronic configuration as a noble gas.

Electrostatic forces of attraction hold ionic compounds together. These are strong forces between oppositely charged positive and negative ions.

The magnesium ion has a charge of 2+. The charge on an ion is equal to the number of electrons lost or gained.

In a dot-and-cross diagram of an ionic compound, brackets are used around each ion to show that the charge is spread evenly over the ion.

True.

Chlorine gains one electron to form a chloride ion (Cl^-). It therefore has one more electron than protons, giving it a negative charge.

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

Ionic compounds have high melting and boiling points because there are strong electrostatic forces of attraction between oppositely charged ions acting in all directions, requiring a large amount of energy to overcome.

False.

In the solid state, ions are in fixed positions in the lattice and cannot move. Ionic compounds conduct electricity only when molten or dissolved in water, because the ions can then move and carry a charge.

When an ionic compound is melted or dissolved in water, the ions are free to move and carry a charge, allowing the compound to conduct electricity.

Magnesium oxide has a higher melting point than sodium chloride because Mg²⁺ and O^2- ions carry a greater charge than Na⁺ and Cl^- ions, resulting in stronger electrostatic forces of attraction that require more energy to overcome.

True.

Electrostatic forces between oppositely charged ions act in all directions throughout the giant ionic lattice. This is what makes ionic compounds have high melting points.

An electrostatic force of attraction is the force between oppositely charged particles. In ionic compounds, it acts between positive and negative ions and holds the giant lattice structure together.

The greater the charge on the ions in an ionic compound, the stronger the electrostatic forces and the higher the melting point.

A covalent bond is the electrostatic attraction resulting from the sharing of a pair of electrons between two non-metal atoms.

Only non-metal elements participate in covalent bonding. When non-metal atoms share pairs of electrons, they form covalent bonds.

In a dot-and-cross diagram, electrons from one atom are shown as dots and electrons from the other atom are shown as crosses, with shared electrons in the area of overlap.

True.

In covalent bonding, atoms share electrons so that each atom gains a full outer shell, giving them the same electronic configuration as a noble gas.

A double bond is formed when two adjacent atoms share two pairs of electrons, creating two covalent bonds between them. Carbon dioxide contains double bonds.

Three pairs of electrons are shared in a triple bond. Nitrogen (N₂) is an example of a molecule that contains a triple bond between its two nitrogen atoms.

False.

In covalent bonding, electrons are shared between atoms, not transferred. It is ionic bonding that involves the transfer of electrons.

Covalently bonded substances may consist of small molecules or giant molecules. When two or more atoms bond covalently, they form a molecule.

Intermolecular forces are weak forces of attraction that act between molecules in a simple molecular substance. They are much weaker than the covalent bonds within the molecules.

Simple molecular substances have low melting and boiling points because the intermolecular forces between molecules are weak and require very little energy to overcome.

False.

When a simple molecular substance melts, it is the weak intermolecular forces between molecules that are overcome, not the strong covalent bonds within the molecules.

Simple molecular structures contain two types of bond: covalent bonds between the atoms within each molecule, and intermolecular bonds between the molecules.

Larger simple molecules tend to have higher boiling points because as molecule size increases, the strength of the intermolecular forces increases, so more energy is needed to overcome them.

True.

Simple molecular substances are poor conductors of electricity because there are no free ions or electrons to move and carry a charge.

Simple molecular structures consist of molecules containing only a few atoms held together by covalent bonds, with weak intermolecular forces between the molecules. Carbon dioxide and methane are examples.

Common insulators like rubber and wood are covalent molecules that do not allow a flow of charge because there are no free ions or electrons.

A giant covalent structure is a lattice containing billions of non-metal atoms, each joined to adjacent atoms by strong covalent bonds. Diamond and graphite are examples.

In diamond, each carbon atom is bonded to four other carbon atoms in a tetrahedral arrangement, forming very strong, identical covalent bonds throughout the structure.

False.

Diamond cannot conduct electricity because all four outer-shell electrons of each carbon atom are used in covalent bonds, leaving no free electrons to carry a charge.

In graphite, each carbon atom is bonded to three others, forming layers of hexagons, with one delocalised electron per carbon atom.

Graphite is slippery because it is arranged in layers held together by weak intermolecular forces. These layers can slide over each other easily, making graphite useful as a lubricant and in pencils.

True.

Both diamond and graphite have giant covalent structures with strong covalent bonds between carbon atoms that require a large amount of energy to break, giving both substances high melting points.

Graphite conducts electricity because each carbon atom bonds to only three others, leaving one delocalised electron per atom. These delocalised electrons move through the structure and carry a charge.

Diamond is extremely hard because each carbon atom forms four strong covalent bonds, making it useful in cutting tools like drills.

Fullerenes are cage-like structures made entirely of carbon atoms. They include buckminsterfullerene (C₆₀) and carbon nanotubes.

The molecular formula of buckminsterfullerene is C₆₀. It consists of 60 carbon atoms arranged in 20 hexagons and 12 pentagons forming a hollow sphere.

True.

Fullerenes can trap other molecules inside their hollow cage structure, which makes them useful for targeted drug delivery systems.

Buckminsterfullerene consists of 60 carbon atoms arranged in 20 hexagons and 12 pentagons to form a hollow sphere.

Fullerenes are useful for supporting catalyst molecules because they have a huge surface area, which allows catalyst molecules to be trapped on their surfaces where they are easily accessible to reactants.

True.

Some fullerenes are excellent lubricants because the intermolecular forces between individual fullerene molecules are weak, allowing them to slide past each other easily.

Buckminsterfullerene is a fullerene made of 60 carbon atoms (C₆₀) arranged in a hollow spherical cage, resembling a soccer ball with 20 hexagons and 12 pentagons.

Fullerenes have a huge surface area, making them useful for trapping catalyst molecules to speed up chemical reactions.

Graphene is a single layer of graphite consisting of carbon atoms covalently bonded in a continuous hexagonal arrangement. It is essentially a 2D molecule, one atom thick.

Graphene conducts electricity because it has delocalised electrons that are free to move through the structure and carry a charge.

True.

Graphene is extremely strong and light because it has an unbroken pattern of strong covalent bonds between carbon atoms. It is considered one of the strongest materials known.

Carbon nanotubes are produced by rolling a sheet of graphene into a cylinder. They have high tensile strength and low density.

Carbon nanotubes have a high melting point because they contain strong covalent bonds between carbon atoms that require a large amount of energy to overcome.

False.

Carbon nanotubes have a much smaller scale structure than carbon fibres and are not used in the manufacture of bikes and tennis rackets.

A carbon nanotube is a type of fullerene formed by rolling a graphene sheet into a cylinder. It has high tensile strength, low density, and conducts electricity.

In a carbon nanotube, each carbon is bonded to three others, leaving one delocalised electron per atom that can carry a charge.

Bulk properties are characteristics of a material such as melting point, electrical conductivity, flexibility, and hardness. They arise from the type and strength of bonds present and how atoms are arranged.

Diamond is extremely hard because each carbon atom is bonded to four others by strong covalent bonds throughout the structure. Graphite is soft and slippery because it forms layers with weak intermolecular forces between them, allowing the layers to slide.

False.

Individual carbon atoms do not possess bulk properties such as hardness or conductivity. These properties arise from the type and strength of bonds and the arrangement of many atoms together.

Bulk silver is a shiny and malleable metal used mainly in jewellery, whereas silver nanoparticles have antibacterial and antifungal properties.

Graphene is almost transparent and conducts both electricity and heat. It also has extremely high strength, making it useful in composite materials and electronics.

True.

Carbon nanotubes have a high tensile strength because every carbon atom is joined to others by strong covalent bonds that require a large force to break.

The bulk properties of a material depend on the type and strength of the bonds it contains, and how the atoms are arranged.

Two bulk properties that fullerenes have but diamond does not are:\n\n1. Can conduct electricity\n2. Are slippery\n\nDiamond cannot conduct electricity and is not slippery. These differences arise from the different structures and bonding arrangements in each allotrope.

Nanoparticles are particles between 1 and 100 nanometres in size. They have a very high surface area to volume ratio.

Nanoscience is the research into the production and application of nanoparticles. It studies how nanoparticles behave and how their properties can be used in technology and medicine.

True.

As particles get smaller, the surface area to volume ratio increases. This is why nanoparticles may have very different properties compared to the same material in bulk form.

Silver nanoparticles have antibacterial and antifungal properties, making them useful in sports clothing to prevent body odour.

Titanium dioxide nanoparticles are used in transparent sunscreens because they reflect UV light to protect skin from sunburn, while being too small to be visible on the skin surface, making the sunscreen appear transparent.

False.

The use of nanoparticles is at an early stage and the long-term health effects are not yet well understood. Nanoparticles are small enough to potentially enter cells or the bloodstream, raising concerns that require further research.

Titanium dioxide nanoparticles are used in self-cleaning windows, where they break down dirt on the surface when UV light shines on them.

Silver nanoparticles are used to:\n\n1. Clean surgical equipment by killing bacteria on surfaces\n2. As an antibacterial coating inside fridges to kill bacteria that cause odours

Smart materials are materials that can have their properties changed in a reversible way in response to a change in conditions, such as temperature or light.

Photochromic pigments are materials that change colour depending on light intensity. They are used in photochromic lenses that darken in UV light to act as sunglasses and return to clear when indoors.

True.

Thermochromic pigments change colour as temperature changes. They are used in colour-changing mugs and strip thermometers.

Polymer gels can absorb up to 1000 times their own volume in water. They are used in nappies and in soil granules to help plants retain water.

Shape-memory alloys used in surgical bone plates revert to their original shape when warmed by the body. This applies tension across the fracture site, which helps bone heal more quickly.

False.

Shape-memory polymers can be bent out of their original shape but revert back to it when heated. This reversibility is what makes them useful in applications like car bumpers and gum-shields.

Shape-memory alloys are metal mixtures that can revert to their original shape when heated. They are used in applications such as surgical bone plates, helmets, and car bodies.

Photochromic lenses darken when exposed to UV light and return to clear when removed from sunlight, making them suitable as both normal glasses and sunglasses.