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Chapter 5
Chemical Bonding
| Question | Answer |
|---|---|
| What is a compound | A compound is a substance that is made up of two or more different elements combined together chemically |
| How do atoms form compounds | To do this atoms use their electrons to form chemical bonds. |
| What are chemical bonds | Chemical bonds are strong attractive forces holding atoms or ions together. |
| What is the octet rule | Octet Rule: When bonding occurs, atoms tend to reach an electron arrangement with eight electrons in the outermost energy level. |
| Why do elements combine | Elements combine in order that their atoms can achieve a stable electronic configuration. |
| Why do atoms tend to follow the octet rule | In order to gain stability atoms tend to follow a rule called the octet rule. |
| What are the two exceptions to the octet rule | Elements near helium (e.g. hydrogen, lithium) want to have two electrons in their outer energy level, not eight Transition metals don’t follow the octet rule since they have variable valency. |
| When atoms gain or lose electrons, what do they become and what type of bond do they have | When they gain or lose electrons, atoms become ions and the forces of attraction between the oppositely charged ions are called ionic bonds. |
| When atoms share electrons, what do they become and what type of bond do they have | When atoms share electrons, they form molecules and the bonds between atoms in a molecule are called covalent bonds. |
| What does valency mean | Valency is a measure of how many bonds an atom will form to satisfy the octet rule. |
| Predicting valency chart | Group --I II III IV V VI VII VIII Valency 1 2 3 4 3 2 1 0 |
| What is Ionic bonding | Ionic bonding is the force of attraction between oppositely charged ions. Ionic bonding generally occurs between a metal and non-metal. The metal donates an electron to become a cation, while the non-metal gains an electron to become an anion. |
| What are the 10 polyatomic ions you need to memorise as you cannot figure them out the normal way | Name Formula Charge Ammonium NH₄⁺ +1 Hydroxide OH⁻ –1 Nitrate NO₃⁻ –1 Carbonate CO₃²⁻ –2 Hydrogen carbonate (Bicarbonate) HCO₃⁻ –1 Sulfate SO₄²⁻ –2 Sulfite SO₃²⁻ –2 Phosphate PO₄³⁻ –3 Chlorate ClO₃⁻ –1 Permanganate MnO₄⁻ –1 |
| What is covalent bonding | A covalent bond is formed when electrons are shared between two atoms. Covalent bonding generally occurs between non-metals. |
| What are elements that exist as covalent bonds called and what are they | diatomic molecules. H₂ (hydrogen) N₂ (nitrogen) O₂ (oxygen) F₂ (fluorine) Cl₂ (chlorine) Br₂ (bromine) I₂ (iodine) |
| When is a single covalent bond formed | A single covalent bond is formed when one pair of electrons is shared between two atoms. |
| When is a double covalent bond formed | Double covalent bonds can be formed when two pairs of electrons are shared between two atoms |
| When is a triple covalent bond formed | A triple bond is formed when three pairs of electrons are shared. |
| What is an intramolecular bond | Intramolecular bonds are the bonds (between atoms) in a molecule. |
| What is an intermolecular force | Intermolecular forces are the forces of attraction that exist between molecules. |
| What is electronegativity | Electronegativity is the relative attraction that an atom in a molecule has for a shared pair of electrons in a covalent bond. |
| What is a molecule | A molecule is a group of atoms joined together. It is the smallest particle of an element or compound that can exist independently. |
| How do you discern between an Ionic and covalent bond using electronegativity values | The general rule is that if the difference in electronegativity values between two atoms is greater than 1.7, they form an ionic bond. If it’s less than 1.7, they form a covalent bond. |
| What are the two types of covalent bonds | pure (non-polar) and polar. |
| What happens when atoms share electrons unequally | The atom which is more electronegative will be partially negative as it has a stronger pulling force on the electrons which means it has more of the electrons making it more partially negative while the other atom will be partially positive |
| what happens when two atoms have the same electronegativity | The electrons are shared equally. Neither atom needs a δ+ or δ−. This is a pure covalent bond (also called a non-polar covalent bond, as there are no opposite ‘poles’ of charge within the molecule). |
| How can you predict what type of covalent bonding is present using electronegativity values | smaller than 0.4 = pure/non polar or slightly polar bigger than 0.4 to less than 1.7 = polar |
| what physical properties of compounds can be attributed to he type of bonding present | electrical conductivity melting and boiling points state of matter at room temperature solubility in water |
| electrical conductivity | Ionic compounds contain ions, They will conduct electricity when those ions are free to move ionic compounds don’t conduct electricity when in solid form Covalent compounds don’t conduct electricity, made of neutral molecules. |
| melting and boiling points | Ionic compounds typically have high melting points due to the strong ionic bonds between their ions. Covalent compounds have relatively low melting and boiling points since the energy needed to separate molecules is the energy needed to weaken the |
| melting and boiling points | intermolecular forces, not the covalent bonds in a molecule. Therefore, the melting or boiling points depend on the type of intermolecular force between molecules and the strength of this force. |
| solubility in water - Covalent | For covalent compounds, the general rule is that like dissolves like – i.e. polar solvents dissolve polar solutes, and pure (non-polar) solvents dissolve pure (non-polar) solutes. |
| solubility in water - Ionic | Ionic compounds can dissolve in water because the ionic bonds in their compounds are overcome by the strong attraction between the ions and the polar water molecules. |
| How do you represent electrons on a lewis diagram | dots and crosses |
| How do you represent lone pairs and shared pairs on a lewis diagram | In a Lewis diagram, shared pairs of electrons are drawn as lines, and lone pairs of electrons (electrons that aren’t shared but belong to only one atom) are drawn as dots. |
| What are sigma bonds | Sigma bonds are formed when atomic orbitals overlap head-on. |
| What is an orbital overlap | To form a molecule of hydrogen, H2, the 1s orbital of each atom overlaps When two atomic orbitals overlap, they form a molecular orbital, with both electrons attracted to both nuclei. These overlaps of atomic orbitals can be head-on or sideways. |
| What are Pi bonds | Pi bonds are formed when atomic orbitals overlap sideways. |
| Are sigma bonds or Pi bonds stronger | Sideways overlap is less efficient than head-on overlap, so pi bonds are weaker than sigma. |
| Single bonds are made of which bonds (Pi or Sigma) | All single bonds are sigma bonds (single = sigma). |
| Double bonds are made of which bonds (Pi or Sigma) | A double bond is composed of one sigma bond and one pi bond. It’s stronger than a single bond but not twice as strong, since pi bonds are weaker than sigma bonds. |
| Triple bonds are made of which bonds (Pi or Sigma) | A triple bond is made of one sigma bond and two pi bonds (and is stronger than both single and double bonds). |
| What are delocalised electrons | Delocalised electrons are electrons shared between more than two atoms – i.e. not associated with a single atom or bond. |
| What are the limitations of predicting bonding between atoms | Using electronegativity is not always reliable Not all bonds are purely ionic or covalent Variable Valency Polyatomic Ions |
Created by:
21JulianM
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