Chemical BONDING 3.2

Learning objectives Be able to define bonding and explain the need to bond? Describe the different bonding types? Ionic Covalent Polar – Covalent Metallic How to predict bonding preference for elements? Relate type of bonding to properties of molecules Relate properties of substances to their uses Be able to suggest the type of structure of a substance given its properties

Electronic configuration and Lewis dot structure Video https://www.youtube.com/watch?v=o4J9mLbvWJA

What is a chemical bond ? Bond is a force of attraction that holds atoms together. Electrons in atoms are responsible for holding them together. Bonding is a way to gain stability.

There are mainly three types of bonds: 1. Ionic bond 2. Covalent bond macromolecules 3. Metallic bond

How to predict bonding preference? You can tell what type of bonding is in a substance by looking at whether the elements in it are metals or non-metals:   METAL NON-METAL Metallic bond  Ionic bond  Covalent bond 

Starter Sort the compounds below into groups within the circles below according to their chemical bonding; Sodium chloride, NaCl Magnesium, Mg Methane, CH4 Magnesium oxide, MgO Aluminium, Al Caesium, Cs Barium iodide, BaI2 Oxygen, O2 Ammonia, NH3 Ionic Covalent Metallic

Starter Complete the starter sheet – Which type of chemical bond. CH4 Ionic Covalent Metallic NaCl BaI2 MgO CH4 O2 NH3 Mg Al Cs

Ionic bond

Definition Ionic bonding is a type of chemical bonding that involves the electrostatic attraction between oppositely charged ions. These ions represent atoms that have lost one or more electron (known as cations) and atoms that have gained one or more electrons (known as an anions). In the simplest case, the cation is a metal atom and the anion is a nonmetal atom

Example-Ionic Bonding

Try and draw diagrams to show how the following combinations would bond together Lithium and chlorine Calcium and oxygen Potassium and bromine Magnesium and fluorine Magnesium and oxygen Beryllium and oxygen Calcium and chlorine

Properties of ionic compounds Crystalline solids made of ions High melting/boiling points Solids at room temperature and strong electrostatic bonds Many are soluble in water Ions separate when dissolved in water Liquids & Solutions → Good Conductors Ions are separated – any substance that has separate charges allow for conduction of electricity Solids → Poor conductors No separation of ions

Giant Ionic compounds Ionic bonding always results in giant ionic structures. These are closely packed, regular arrangements of ions where there are very strong forces of attraction between all the ions in all directions. The strong bonds between all the atoms cause ionic structures to have high melting and boiling points. They will, however, eventually melt and when they do, or when they are dissolved, they are able to conduct electricity. This is because the ions can carry charge and are free to move.

Your task Complete the questions below. Remember to answer in full sentences. 1. Copy and complete: Ionic compounds have ______________ melting points and boiling points because of the strong electrostatic forces of ______________ between ___________ charged ions in the giant _____________. Ionic compounds will ____________ electricity when ____________ or in _____________ because the ions are able to _________ freely. 2. Why is seawater a better conductor of electricity than water from a freshwater lake?

Covalent bond

Definition- Covalent Bond A covalent bond is a chemical bond that involves the sharing of electron pairs between atoms. Atoms can share one, two or three pairs of electrons to form single, double or triple bonds respectively.

Example- Covalent Bond

Non – Polar Covalent bond

Polar Covalent Bonds

Simple covalent Molecules Covalent bonds can result in the formation of simple covalent molecules. Water H2O Methane CH4 Carbon Dioxide CO2 Hydrogen H2 Ammonia NH3

Simple covalent Molecules Substance Melting Point (˚C) Boiling Point (˚C) State at room temperature Water 99.98 Liquid Carbon Dioxide -78 -57 Gas Methane -164 -182 Hydrogen -259.1 -252.8 Ammonia -77.73 -33.34 If we look at the data, we can see that the simple covalent molecules here are all gases or liquids at room temperature. They all have very low melting and boiling point. So why is this if covalent bonds are so strong?

Intramolecular vs. intermolecular Intramolecular forces are the bonds that occur between atoms. These bonds are very strong and require lots of energy to break them. Intermolecular forces are those forces between molecules. Between simple covalent molecules, these bonds are very weak.

Simple covalent Molecules Because the intermolecular forces are so weak, the molecules are easily parted from each other, hence the low boiling and melting points. It is these intermolecular forces that are broken when a compound boils/melts. The covalent bods themselves do not break.

Properties of covalent compounds Gases, liquids, or solids made of molecules, the bonds are comparatively weaker Lower Melting Points than ionic compounds Intermolecular Forces aren’t as strong as interionic forces Cannot conduct electricity as solid, liquid, or when dissolved molecules will not separate into ions Will dissolve in liquids with similar molecular polarity but not in water. e.g. Benzene, chloroform etc. “Like dissolves like”

Your Task Complete the questions below. Remember to answer in full sentences. 1. Copy and complete: Non-metals react to form ________ which are held together by _______ bonds. These hold the atoms together very _________. The forces between molecules are relatively weak, so these substances have low ______ and ________ points. 2. A compound called sulfur hexafluoride (SF6) is used to stop sparks forming inside electrical switches designed to control large currents. Explain why the properties of this compound make it particularly useful in electrical switches. 3. The melting point of hydrogen chloride is -115C whereas sodium chloride melts at 801C. Explain why.

Try and draw diagrams to show how the following combinations would bond together Cl2 H2O CH4 NH3 HCl N2 C2H4 CH3OH CO2

Giant covalent structures Covalent bonding does not always result in simple molecules. Atoms that bond covalently can also form giant structures or macromolecules. Diamond, graphite and silicon dioxide are examples of giant covalent structures of atoms.

Diamond Diamond is the hardest naturally occurring material known to man. The reason for this property can be explained by the bonding within it. Each carbon atom forms four covalent bonds with other carbon atoms to make a very rigid, giant covalent structure. Diamond has extremely high melting and boiling points and is used for jewellery and drill tips.

Graphite Carbon can also bond slightly differently to form graphite. In graphite, the carbon atoms arrange themselves to form layers. The layers can slide over each other easily, making graphite ideal for pencils and industrial lubricant. Each carbon is bonded to three others, making flat hexagonal shapes. This leaves one electron left over which becomes delocalised and can move between the layers – these electrons allow graphite to conduct electricity and heat like metals.

Silicon dioxide Sometimes called Silica. This is what sand is made from. It is one giant structure of silicon and oxygen. It can be melted down with sodium carbonate and limestone to make glass.

Your task Complete the questions below. Remember to answer in full sentences. 1. Copy and complete: Giant covalent structures contain many __________ joined by covalent bonds. They have _________ melting points and ___________ points. Diamond is a very __________ substance because the ___________ atoms in it are held strongly to each other. Graphite, however, is ___________ because there are __________ of atoms which can __________ over each other. 2. Graphite is sometimes used to reduce friction between two surfaces that are rubbing together. How does it do this? 3. Explain in detail why graphite can conduct electricity but diamond cannot.

Giant Ionic compounds Ionic bonding always results in giant ionic structures. These are closely packed, regular arrangements of ions where there are very strong forces of attraction between all the ions in all directions. The strong bonds between all the atoms cause ionic structures to have high melting and boiling points. They will, however, eventually melt and when they do, or when they are dissolved, they are able to conduct electricity. This is because the ions can carry charge and are free to move.

Your task Complete the questions below. Remember to answer in full sentences. 1. Copy and complete: Ionic compounds have ______________ melting points and boiling points because of the strong electrostatic forces of ______________ between ___________ charged ions in the giant _____________. Ionic compounds will ____________ electricity when ____________ or in _____________ because the ions are able to _________ freely. 2. Why is seawater a better conductor of electricity than water from a freshwater lake?

Ionic compounds Covalent Your Task - Compare and Contrast the properties of Ionic and Covalent compounds using a Venn Diagram. PROPERTY Volatility Solubility Electrical Conductivity Boiling Point Melting Point

Metallic bond

Why and how are metallic bonds formed? https://www.youtube.com/watch?v=Bi0rUNV8mEw (2:54) Alloys -http://www.youtube.com/watch?v=9LHDSB1n11k

properties of metals Metals are electron donors and form positive ions while bonding. The metallic bond accounts for many physical characteristics of metals, such as strength, malleability, ductility, luster, conduction of heat and electricity.

Properties of metals Melting and Boiling Points metals have high melting and boiling points because of the strength of the metallic bond. The strength of the metallic bond depends on the number of electrons in the delocalized 'sea' of electrons.  (More delocalized electrons results in a stronger bond and a higher melting point.) packing arrangement of the metal atoms.  (The more closely packed the atoms are the stronger the bond is and the higher the melting point.)

Malleable and Ductile Metals are malleable and ductile Malleable and Ductile Metals are malleable and ductile. The delocalized electrons in the 'sea' of electrons in the metallic bond, enable the metal atoms to roll over each other when a stress is applied. Optical Properties Metals typically have a shiny, metallic lustre. Photons of light do not penetrate very far into the surface of a metal and are typically reflected, or bounced off, the metallic surface.

To Recapitulate

Metallic Structures Metals consist of giant structures of atoms arranged in a regular pattern. Each metal atom ‘loses’ it’s outer electrons which become free to move throughout the metal atoms (we say they are delocalised). These delocalised electrons hold the atoms together in a regular structure (acting a bit like a glue).

Metallic structures The free electrons in metals are the reason that most metals can conduct electricity and conduct heat. They also allow the atoms to slide over each other, causing metals to be malleable.

Good electrical conductor? YOUR task Four substances were tested for various properties with the following results: Identify the type of bonding in each substance, giving reasons for your answers. Substance Melting Pt (C) Boiling Pt (C) Good electrical conductor? A -218.4 -182.96 No B 1535 2750 Yes C 1410 2355 D 801 1413 When molten

Making metals harder An alloy is a mixture of two or more elements, one of which is a metal. Alloys usually have different properties that are different to the metals they contain. This makes them more useful than the pure metals alone. For example, they may be harder than the pure metal. Alloys contain atoms of different sizes which distorts the layers, preventing the layers from sliding over each other.

Nanoscience The science of structures that are 1-100nm in size (just a few hundred atoms) Nanoparticles have different properties to the same ‘bulk’ materials e.g. silver has no antibacterial properties in bulk, but can be used in antibacterial plasters etc as nanoparticles as they take on these special properties. Nanoparticles have an extremely high surface area to volume ratio Uses include – new computers, new catalyst, new coatings, sensors, stronger lighter construction materials, cosmetics, sun creams.

Important links https://www.youtube.com/watch?v=zpaHPXVR8WU https://www.youtube.com/watch?v=TxHi5FtMYKk https://www.youtube.com/watch?v=OQ-pcxo-Q5c https://www.youtube.com/watch?v=X9FbSsO_beg https://www.youtube.com/watch?v=S08qdOTd0w0 https://www.youtube.com/watch?v=JPH5-fCxX-Q