3.1.3 - bonding Flashcards
Define electronegativity
The ability of an atom to attract electron density in a covalent bond
State intermolecular forces in order of strongest to weakest
- Hydrogen bonds
- Dipole-Dipole forces
- Van der Waals forces
Describe how a hydrogen bond forms
- between H atom and a Nitrogen, Fluorine or Oxygen atoms lone pair
- sandwich of the H atom must be linear, due to electrostatic repulsion
How does hydrogen bonding effect sold structures
- ice is less dense than water
- liquid, H bonds constantly broken and remade due to constant movement
- when cooled to ice, molecules slow
- arrange into ordered structure, allows H bonds to form in a linear structure
- molecules held further apart in ice
Describe how dipole dipole forces form
- between molecules with a permanent dipole
- δ+ and δ- regions attract each other
- dipoles align due to electrostatic repulsion
Describe how Van der Waals forces form
A molecules instantaneous dipole induces a dipole on another molecule
Describe how an instantaneous dipole occurs
- due to random electron movement around a stationary nucleus
- one side of an atom can become δ- (due to e’s)
- the other side is therefore δ+
Describe why boiling points increase down a group
- the Mr of an atom increases, meaning the number of electrons increases
- this means greater induced dipoles
- therefore, VDW’s between molecules is stronger, which require more energy to break
Name the 4 types of crystal structure
- ionic
- metallic
- macromolecular
- molecular
Describe what ionic bonding is
- electrostatic attraction between positively charged ions and negatively charged ions
- electrons transferred between metals and non-metals
Explain properties of ionic compounds
- high melting and boiling point, due to strong electrostatic forces
- can only conduct electricity when molten or aqueous, as ions are free to move and carry a charge
Describe metallic bonding
Attraction between a lattice of positive ions and their delocalised outer shell electrons
How is the strength of an ionic compound determined
- based on charge density
- greatest charges for the smallest sized ions result in higher strengths
What is charge density
= charge/size
- charge depends on the group in periodic table
- size of the ion increases down a group
Explain the properties of metallic structures
- do not dissolve, as they often react with water
- conduct electricity in any form, as there is a sea of delocalised electrons which can move and carry a charge
What determines a metallic structures strength
- charge density
- the higher the charge for smaller metal ions will result in a greater attraction between the cation and the delocalised electrons
Describe how molecular substances bond
- “2 non-metals sharing pair(s) of electrons
- atoms within the molecule are held together by covalent bonds
- individual molecules are held together by weak intermolecular forces
Explain the properties of molecular structures
- low boiling + melting point, due to the weak intermolecular forces
- cannot conduct electricity, due to no delocalised electrons
Describe a macromolecular substances structure
- thousands of atoms in a lattice structure
- held together by covalent bonds
Explain the properties of a macromolecular substance
- high melting + boiling point, due to strong covalent bonds that must be broken
- graphite and graphene can conduct electricity , due to delocalised electrons
- others can’t conduct electricity
Outline the “exceptions to the octet rule” within covalent bonding
- some elements may end up having more than 8 electrons in their outer shell once covalently bonded
- some elements with few electrons may have less than 8 electrons in their outer shell once covalently bonded within a compound
Why do some elements have more than 8 electrons in their outer shell once they are in a covalent compound
- the d sub shell is close in energy to other sub shells
- this allows electrons within it to move between sub shells
What is a dative covalent bond
- when the shared pair of electrons comes from one atom only
Describe the VSEPER theory
- Valence shell electron pair repulsion theory
- predicts the shape of a molecule based on the no. of electron pairs surrounding the central atom
- lone pairs and bonding pairs affect the molecules bond angle / shape
