Edexcel Chemistry A-level Bonding and Structure Notes PDF

# Edexcel Chemistry A-level - Topic 2: Bonding and Structure ## Topic 2A: Bonding ### Ionic Bonding - Ionic bonding occurs between a **metal** and a **non-metal**. - Electrons are **transferred** from the metal to the non-metal to form full outer shells. - **Transfer** of electrons creates **cha...

# Edexcel Chemistry A-level - Topic 2: Bonding and Structure ## Topic 2A: Bonding ### Ionic Bonding - Ionic bonding occurs between a **metal** and a **non-metal**. - Electrons are **transferred** from the metal to the non-metal to form full outer shells. - **Transfer** of electrons creates **charged particles** called **ions**. - **Oppositely charged ions** attract through electrostatic forces to form a **giant ionic lattice**. #### Example: - Sodium chloride is an ionic compound formed from **Na+** and **Cl-** ions. - Sodium **loses** an electron and chlorine **gains** an electron to produce ions with a full outer electron shell. - They then form an **ionic lattice** with **strong electrostatic attraction** between oppositely charged ions. #### Important Considerations: - The **charge** of an ion is related to the **strength** of the ionic bond that forms. - Ions with a **greater charge** will have a **greater attraction** to the other ions resulting in **stronger forces of attraction** and therefore **stronger ionic bonding**. - **Larger ions** that have a **greater ionic radius** will have a **weaker attraction** to the oppositely charged ion because the attractive forces have to act over a **greater distance**. - **Cations** (+ve) and **anions** (-ve) can be represented using **dot and cross diagrams** and so can ionic bonding. The electrons being transferred from the cation can be seen on the outer shell of the anion. ### Covalent Bonding - Covalent bonds form between **two non-metals**. - There is a **strong electrostatic attraction** between the two nuclei and the **shared electrons** between them. - Electrons are **shared** between the **two outer shells** in order to form a **full outer shell.** - **Multiple electron pairs** can be shared to produce **multiple covalent bonds.** #### Representation: - The shared electron pairs can be represented using **dot and cross diagrams**. - The overlap includes a **covalent bond**. - The **number of electrons** within the overlap tells you the **nature** of the covalent bond: - **2 electrons** (1 from each atom): **single bond**, displayed formula represented as - - **4 electrons** (2 from each atom): **double bond**, displayed formula represented as = - **6 electrons** (3 from each atom): **triple bond**, displayed formula represented as = #### Important Considerations: - **Double and triple bonds** can also be shown on dot and cross diagrams with the **multiple electron pairs** being displayed in the **shared segment** between the two atoms. - The **length** of a covalent bond is strongly linked to its **strength**. - **Shorter bonds** tend to be **stronger** as the atoms are held closer together so the forces of attraction are greater, requiring more energy to be overcome. - **Double and triple bonds** are **shorter** than single covalent bonds, explaining why they are so much stronger. ### Dative Bonding - Dative or coordinate bonds form when **both** of the **electrons in the shared pair** are supplied from a **single atom**. - It is indicated using an **arrow** from the **lone electron pair**. #### Example: - Ammonia (NH3) has a **lone electron pair** that can form a **dative bond** with a **H+** ion to produce an ammonium ion (NH4+). #### Important Considerations: - Once a dative bond has formed, it is **treated as a standard covalent bond** as it reacts in **exactly the same way** and has the **same properties** regarding length and strength. - Since **both electrons** come from the **same atom** in a **dative covalent bond**, in **dot and cross diagrams** both electrons in that bond **will have the same shape.** - In other words, they will **both** be dots or **both be crosses.** ### Simple Covalent - Substances with a simple molecular structure consist of **covalently bonded molecules** held together with **weak van der waals forces**. - These are a type of **intermolecular force** that act **between the molecules** holding them in a structure. #### Example: - Iodine (I2) ## Topic 2B: Structure ### Bonding and Physical Properties - The physical properties of a substance include its **boiling point**, **melting point**, **solubility** and **conductivity**. - They are different depending on the **type of bonding** present, the types of particle present, and the **crystal structure** of the compound. ### Crystal Structures - There are **four main** types of **crystal structure**: - **Ionic** (e.g. Sodium Chloride) - **Metallic** (e.g. Aluminium) - **Simple molecular** (e.g. Water) - **Macromolecular** (e.g. Diamond) ### Ionic (e.g. Sodium Chloride) - Substances with an **ionic crystal structure** have a **high melting and boiling point**. - This is because the **electrostatic forces** holding the **ionic lattice together** are **strong** and require a lot of energy to overcome. - When **molten** or **dissolved in solution**, ionic substances **can conduct electricity**. - In this state, the ions **separate** and are **no longer held** in a lattice. - Therefore, they are **free to move** and carry a **flow of charge**, so **can conduct an electrical current**. - Ionic substances are often **brittle materials**. - When the **layers of alternating charges** are distorted, **like charges repel**, breaking apart the **lattice into fragments**. ### Metallic (e.g. Aluminium) - Substances with **metallic structures** are often **good conductors**. - The **delocalised electrons** are able to **move** and carry a **flow of charge**. - Metals are also **malleable** as the layers of **positive ions** are able to **slide over one another**. ### Simple molecular (e.g. Water) - Substances with a **simple covalent molecular structure** consist of **covalently bonded molecules** held together with **weak van der waals forces**. - This is the structure formed by water and iodine, I2. - These **van der waals forces** are very weak, and not **much energy** is required to overcome them. - This means simple molecular substances have **low melting and boiling points**. - Simple molecular substances are **very poor conductors** as their structure contains **no charged particles**. ### Giant Covalent Structures - Macromolecular covalent substances are **covalently bonded into a giant lattice structure**. - Each atom has **multiple covalent bonds** which are **very strong**, giving the substance a **very high melting point**. #### Diamond - Diamond is a **macromolecular structure** made up of **carbon atoms** each **bonded to four other carbon atoms**. - This forms a **rigid tetrahedral structure**, making **diamond** one of the **hardest, strongest materials** known. - It is often used on the **tips of drills**. #### Graphite - Graphite is another **macromolecular structure** made up of **carbon atoms**. - However, in graphite, each carbon atom is **bonded to three others** in flat hexagonal sheets. - This means there is **one delocalised electron per carbon atom**. - These electrons **can move freely**, allowing **graphite to conduct electricity.** - Graphite can therefore be used in an **electrode**. - The **intermolecular forces** between layers of graphite are **weak**, allowing the layers to easily slide over each other, meaning **graphite can be used as a lubricant**. #### Graphene - Graphene consists of **single, 2D sheets of graphite** that are just **one atom thick**. - These sheets are formed of **hexagonal carbon rings** that create a **very strong, rigid material** that is **extremely lightweight**. - **Delocalised electrons** move through each layer **allowing it to conduct electricity**, making **graphene** a useful material in electronics.