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

The period number tells you how many electron shells the atom has. For example, an element in Period 3 has three shells of electrons.

False.

The first shell holds a maximum of 2 electrons. The second and third shells each hold a maximum of 8 electrons.

In the electronic configuration 2.8.7, the element is in Period 3 and Group 7.

An electron shell diagram is a drawing that shows the arrangement of electrons in an atom, with electrons placed on concentric circles (shells) around the nucleus.

The group number tells you how many electrons are in the outer shell of the atom. For example, a Group 2 element has 2 electrons in its outermost shell.

True.

Elements in the same group share the same number of outer shell electrons, which is why they have similar chemical properties.

Atoms react because their outermost shell is not full. By gaining, losing, or sharing electrons with other atoms they can achieve a full outer shell, making them more stable.

Potassium has the electronic configuration 2.8.8.1 and is in Group 1 and Period 4.

Noble gases have full outer shells of electrons. This makes them very stable and largely unreactive.

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

Sodium is in Group 1 and has one outer shell electron. Losing that one electron gives it a full outer shell, so the charge is 1+.

True.

These ions gain or lose electrons until they have a full outer shell, which matches the electronic structure of the nearest noble gas.

In magnesium oxide, magnesium forms a 2+ ion and oxygen forms a 2− ion. The formula of the compound is MgO.

An anion is a negatively charged ion formed when an atom gains one or more electrons, so it has more electrons than protons.

A dot and cross diagram shows the transfer of electrons between atoms. Dots and crosses represent electrons from each atom. Each ion is enclosed in square brackets with its charge shown in superscript outside.

False.

For larger atoms with more electron shells, you only need to draw the valence (outer) shell in the dot and cross diagram.

A ball and stick model does not show the charges on ions and places ions unrealistically far apart. It also fails to show the movement of electrons or indicate accurate relative ion sizes.

When a chlorine atom gains one electron it becomes a chloride ion with a charge of 1−.

Ionic bonding requires one species to lose electrons (the metal, forming a cation) and another to gain them (the non-metal, forming an anion). Two metals both tend to lose electrons, so they cannot form an ionic bond with each other.

A covalent bond is a shared pair of electrons between two non-metal atoms, formed so that each atom achieves a full outer shell.

Non-metal atoms both tend to gain electrons to fill their outer shells. Neither atom can donate electrons to the other, so instead they share electron pairs to achieve a full outer shell.

False.

Simple covalent molecules do not conduct electricity because they contain no free electrons or ions to carry charge.

In a water molecule (H₂O), oxygen forms two covalent bonds with hydrogen. The bonding electrons are shared between the atoms.

Lone pairs are pairs of electrons in the outer shell of an atom that are not involved in any covalent bond.

Bonding electrons are shared between two atoms and form the covalent bond. Lone pairs are outer shell electrons that are not shared and remain on a single atom.

False.

In covalent bonding the electrons are shared, not transferred. No ions are formed. Transferred electrons are a feature of ionic bonding.

A molecule of ammonia (NH₃) contains three covalent bonds and one lone pair on the nitrogen atom.

Advantage: shows the 3D shape of the molecule and the difference between single and double bonds.

Disadvantage: does not show how many electrons each atom has or how much space each atom fills.

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

A giant covalent structure is a huge lattice of non-metal atoms all bonded together by strong covalent bonds throughout the structure. There are no separate molecules and no weak intermolecular forces between them.

Giant covalent structures have high melting points because they contain a very large number of strong covalent bonds throughout the lattice. A large amount of heat energy is needed to break these bonds.

False.

Most giant covalent structures cannot conduct electricity because they have no free electrons or charged particles. Graphite and graphene are notable exceptions.

Giant covalent structures are also called giant lattices. They have a fixed ratio of atoms in the overall structure.

Three common giant covalent structures are:

1. Diamond

2. Graphite

3. Silicon dioxide

A simple molecular structure is one containing a small, fixed number of atoms held together by strong covalent bonds. Weak intermolecular forces act between molecules, so these substances are often liquids or gases at room temperature.

Both contain strong covalent bonds, but a simple covalent molecule has a small, fixed number of atoms whereas a giant covalent structure has a large, variable number of atoms bonded throughout a lattice.

True.

Both types of structure contain strong covalent bonds between atoms. The key difference is the number and arrangement of atoms, not the type of bond.

Giant covalent structures are solid at room temperature because there are no weak intermolecular forces to overcome — the entire structure is held together by strong covalent bonds, making it very difficult to separate the atoms.

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

A monomer is a small molecule that acts as a repeat unit and joins to many other monomers to form a polymer chain.

Polymers are solid at room temperature because the intermolecular forces between the long polymer chains are larger than those between simple molecules, making the chains harder to separate.

False.

Some polymers are produced naturally by living organisms. Examples of natural polymers include DNA, proteins, silk and wool.

Polymers are made from a large number of small molecules called monomers. These are joined by strong covalent bonds to form a very large molecule called a macromolecule.

Two synthetic polymers are:

1. Polythene — used in plastic bags

2. PVC — used in water pipes

Three natural polymers are:

1. DNA

2. Proteins

3. Silk (or wool)

True.

Monomers are joined by strong covalent bonds. It is the intermolecular forces between different polymer chains (not the bonds within a chain) that are comparatively weaker.

A polymer is a macromolecule — this term is used because polymers have a very high relative molecular mass due to their extremely long carbon chains made from many repeating monomer units.

Metallic bonding is the strong electrostatic attraction between positive metal ions and a sea of delocalised electrons that move freely throughout the metal lattice.

Delocalised electrons are electrons that are no longer associated with any one specific atom. In a metal, they come from the outer shells of the metal atoms and are free to move throughout the lattice.

Metals can conduct electricity because they contain delocalised electrons that are free to move through the lattice and carry charge.

False.

Outer shell electrons become delocalised and are no longer attached to any specific atom. They move freely between the positive metal ions, forming a "sea" of delocalised electrons.

In a metal, atoms lose their outer shell electrons to form positively charged metal ions. The electrons become delocalised and can move freely, creating strong electrostatic attractions that hold the structure together.

Metals form a giant lattice structure in which positive metal ions are arranged in a regular pattern, surrounded by a sea of delocalised electrons that hold them together.

An alloy is a mixture of two or more metals. Alloys also contain a metallic lattice structure with delocalised electrons, so they exhibit the same type of metallic bonding as pure metals.

True.

The strong electrostatic attraction between positive metal ions and the sea of delocalised electrons requires a large amount of energy to overcome, giving metals high melting points.

Metal atoms become positively charged ions because they lose their outer shell electrons. These electrons become delocalised and are no longer bound to any individual atom, leaving the atom with more protons than electrons.

Mendeleev arranged elements into vertical columns based on their chemical properties and then ordered them horizontally by increasing atomic mass. He left gaps where no known element fitted the pattern.

Mendeleev left gaps because he predicted that undiscovered elements would be found to fill them. He used trends in the surrounding elements to predict the properties of these missing elements.

False.

Mendeleev arranged elements in order of increasing atomic mass, not atomic number. The concept of atomic number was not known at the time.

The group number tells you the number of electrons in the outer shell (valence electrons) of an atom. Elements in the same group have the same number of outer shell electrons and similar chemical properties.

Elements in the same group have the same number of outer shell electrons, which is why they show similar chemical reactions.

Reactivity increases down Group 1 (alkali metals) but decreases down Group 7 (halogens). It is common for trends in reactivity to be opposite for metals and non-metals.

True.

Elements in the same group have the same number of outer shell electrons, which determines how they react. This is why groups share similar chemical behaviour.

Mendeleev did not force every element into a strict order by atomic mass. Where elements did not fit, he left gaps rather than placing them in the wrong group, and he prioritised chemical properties over mass when the two conflicted.

Elements in the same group react similarly because they all have the same number of outer shell electrons. The number of outer shell electrons controls how an element reacts with other substances.

False.

Helium is in Group 0 but has 2 electrons in its outer (and only) shell. It is an exception to the rule that group number equals the number of outer shell electrons.