Bonding (OCR GCSE Combined Science A (Gateway): Chemistry): Flashcards

The period number tells you how many electron shells the atom has. For example, elements in Period 3 have three electron shells.

False.

The first (innermost) electron shell can hold a maximum of 2 electrons. The second and third shells can each hold a maximum of 8 electrons.

In the electronic configuration 2.8.7, the atom has 3 electron shells and 7 electrons in its outer shell.

The group number tells you how many electrons are in the outer shell of the atom. For example, Group 6 elements have 6 outer shell electrons.

Electronic configuration is a way of showing how electrons are arranged in an atom's shells, written as numbers separated by dots or commas starting from the innermost shell (e.g. 2.8.1 for sodium).

Most atoms have an incomplete outer shell, making them unstable. Atoms react to gain, lose, or share electrons so that the outer shell becomes full, which makes them more stable.

True.

Elements in the same group have the same number of outer shell electrons. This gives them similar chemical properties, as chemical reactions involve the gain, loss, or sharing of outer shell electrons.

Electrons first fill the shell closest to the nucleus, which holds a maximum of 2 electrons. The next shells each hold up to 8 electrons.

The atom is in Group 6 (6 outer shell electrons). It needs to gain 2 electrons to fill the outer shell to 8 electrons and become stable.

An ionic bond is a strong electrostatic force of attraction between oppositely charged ions. It forms when a metal transfers electrons to a non-metal.

A sodium ion carries a 1+ charge. Sodium loses its one outer electron, leaving it with more protons than electrons and an overall positive charge.

False.

In ionic bonding, electrons are transferred from a metal atom to a non-metal atom. Sharing electrons occurs in covalent bonding.

Magnesium is in Group 2 and loses 2 electrons to form a magnesium ion with a 2+ charge.

Ions stay together because of strong electrostatic forces of attraction between the oppositely charged cations and anions. These forces act in all directions throughout the structure.

A dot and cross diagram is a model that uses dots and crosses to represent electrons from different atoms, showing how electrons are transferred during ionic bond formation. Each ion is shown in square brackets with its charge.

Advantage: it clearly shows which atom the electrons come from and how they are transferred. Disadvantage: it does not show the 3D arrangement of ions or their relative sizes.

True.

Chlorine has 7 outer electrons and gains 1 to complete its shell. The extra electron makes it more negative than positive, giving a 1− charge. The ion is called chloride.

In sodium chloride, one electron is transferred from the sodium atom to the chlorine atom, forming Na⁺ and Cl^- ions in a 1:1 ratio.

A ball and stick model places ions far apart from each other, when in reality the gaps between ions in an ionic structure are much smaller. It also does not show the charges on the ions.

A covalent bond is a shared pair of electrons between two non-metal atoms. It forms when atoms share electrons to achieve a full outer shell.

Simple covalent molecules do not conduct electricity because they contain no free electrons (or ions). The electrons are all held within the covalent bonds between atoms.

True.

Covalent bonds form when non-metal atoms share pairs of electrons to achieve a full outer shell. In this specification, covalent bonding is only shown between non-metal atoms (hydrogen and elements on the right of the periodic table).

In a covalent bond, the shared electrons are called bonding electrons. Outer shell electrons not involved in bonding are called non-bonding electrons (or lone pairs).

Water contains 2 covalent bonds. Each bond is formed between oxygen and one hydrogen atom, with the oxygen sharing one pair of electrons with each hydrogen.

Intermolecular forces are weak forces of attraction that exist between individual covalent molecules. They are much weaker than the covalent bonds within the molecules themselves.

False.

A dot and cross diagram fails to show the 3D arrangement of atoms. A ball and stick model is better for visualising 3D shape.

The eight molecules are: hydrogen (H₂), chlorine (Cl₂), oxygen (O₂), nitrogen (N₂), hydrogen chloride (HCl), water (H₂O), ammonia (NH₃) and methane (CH₄).

Ammonia (NH₃) has 3 covalent bond(s) and 1 lone pair(s) of electrons on the nitrogen atom.

Advantage: it shows the 3D arrangement of atoms and the shape of the molecule. Disadvantage: it does not show electron movement and places atoms further apart than they really are.

A giant covalent structure is a huge, extended lattice of non-metal atoms all joined by strong covalent bonds, with no separate molecules. Examples include diamond, graphite and silicon dioxide.

True.

Giant covalent structures have high melting and boiling points because they contain many strong covalent bonds throughout the structure. Large amounts of energy are needed to overcome these bonds.

Most giant covalent structures do not conduct electricity because all of their outer shell electrons are involved in strong covalent bonds. There are no free (delocalised) electrons or charged particles available to move and carry a current.

Exceptions include graphite and graphene, which do have delocalised electrons.

Giant covalent structures can also be called giant lattices and have a fixed ratio of atoms in the overall structure.

Giant covalent structures with very high melting points include Diamond, Graphite, and Silicon dioxide (SiO₂). All contain many strong covalent bonds throughout the structure that require large amounts of energy to break.

True.

Both simple covalent molecules and giant covalent structures contain strong covalent bonds. The key difference is that simple covalent molecules have a small and fixed number of atoms, while giant covalent structures have large and variable numbers of atoms bonded together in an extended lattice.

Graphite and graphene are exceptions. Both can conduct electricity because they have free, delocalised electrons that can move and carry charge.

In a giant covalent structure there are no weak intermolecular forces, only covalent bonds, so substances are usually solid at room temperature.

A polymer is a very large covalent molecule (macromolecule) made by joining together large numbers of smaller molecules called monomers, connected by strong covalent bonds.

A monomer is a small molecule that is a repeat unit in a polymer chain. Many monomers join together via strong covalent bonds to form a polymer.

False.

Polymers have high melting points because there are strong intermolecular forces between the long polymer chains. More energy is needed to overcome these forces compared to smaller molecules.

Polymers have a high relative molecular mass and are sometimes called macromolecules.

Synthetic polymers include polythene and PVC. Natural polymers include DNA and proteins (also silk and wool).

Polymers have longer chains than simple covalent molecules, so there are stronger intermolecular forces between the chains. More energy is needed to overcome these forces, giving polymers higher melting points.

True.

DNA, proteins, silk and wool are all natural (biological) polymers produced by living organisms rather than manufactured synthetically.

Each monomer in a polymer chain is a repeat unit and is connected to adjacent units by strong covalent bonds.

Delocalised electrons are outer shell electrons that have left their original metal atoms and are free to move between all the positive metal ions throughout the lattice, forming a "sea" of electrons.

Metals can conduct electricity because they contain delocalised electrons that are free to move throughout the metallic lattice. These electrons carry charge when a voltage is applied.

In a metal, the atoms lose their outer shell electrons and become positively charged metal ions, surrounded by a sea of delocalised electrons.

True.

Metallic bonding is the electrostatic attraction between a lattice of positive metal ions and a sea of delocalised electrons. The electrons are free to move through the structure, which is why metals conduct electricity and heat.

Metals have a giant lattice structure. The positive metal ions are arranged in a regular, repeating pattern with the sea of delocalised electrons moving freely between them.

Yes. Alloys are mixtures of metals and they retain metallic bonding, with positive metal ions held in a lattice by a sea of delocalised electrons.

The metal atoms are held together by strong metallic bonds, forming a lattice structure.

False.

In metallic bonding, metal atoms lose their outer shell electrons, which become delocalised and form a "sea" of electrons. These free electrons are attracted to the positive metal ions, forming the metallic bond.

Mendeleev arranged elements primarily by their chemical properties and then in order of increasing atomic mass. He left gaps for undiscovered elements rather than forcing elements into incorrect positions.

True.

Mendeleev left gaps in his Periodic Table for elements that had not yet been discovered, rather than forcing elements into incorrect positions. He used the properties of surrounding elements to predict the properties of these undiscovered elements.

Mendeleev's table gained acceptance because the elements he predicted to fill gaps, such as germanium (predicted as eka-silicon), were later discovered and found to match his predicted properties closely.

The modern Periodic Table arranges elements in order of increasing atomic number, whereas earlier tables used atomic mass.

The group number tells you the number of electrons in the element's outer shell (valence electrons). This determines how the element reacts chemically.

True.

Elements in the same group have the same number of outer shell electrons. This means they react in similar ways — for example, all Group 1 metals react with water to form an alkali and hydrogen gas.

Group 1 metals become more reactive as you move down the group. The outer electron is further from the nucleus and more easily lost, making reactions more vigorous.

In the Periodic Table, groups are the vertical columns and periods are the horizontal rows.

Early tables sorted elements strictly by atomic mass and ignored chemical properties. This meant some elements ended up in groups that did not share their chemical behaviour.