Chemistry Clinical Sciences 7-10 Flashcards
What is a Chemical Bond?
A CHEMICAL BOND is the attractive force that holds two or more atoms together in a molecule.
What does bonding involve?
The valence electrons.
What do atoms combine? And how can they combine to do this?
Atoms combine to gain STABILITY. Electrons in atoms are arranged in ORBITALS so the atom is the most stable it can be.
In bonding what does the rearrangement of electrons allow both ions and molecules to do? Why?
Allows molecules/ions to have an even lower energy because when electrons transfer at least one of the atoms will fill less sub levels with a lower energy
What is the Octet Rule?
Elements GAIN/LOSE/SHARE electrons to have 8 ELECTRONS in their highest energy level so they have the same electronic configuration as a noble gas.
How many electrons do transition metal have in their highest energy level? What rule does this obey?
18 electrons- 18 electron rule.
What is
electronegativity?
The ability of an atom to ATTRACT the electrons towards itself in a CHEMICAL BOND.
What does electronegativity depend on?
Number of PROTONS in the nucleus.
SIZE of atom.
Amount of SCREENING by inner electron, e.g. amount of SHIELDING between the nucleus and electrons in the highest energy level.
What is the most electronegative element?
Fluorine
What is electronegativity used to do in both covalent and ionic bonding?
Electronegativity is used in COVALENT BONDING to predict POLARITY of BONDS and in IONIC BONDING to see easy an ATOM will TRANSFER ELECTRONS.
What bonding does low electronegativity + low electronegativity show?
Metallic Bonding
What bonding does high electronegativity + high electronegativity show?
Covalent Bonding
What bonding does a large difference in electronegativity show?
Ionic Bonding
When are ionic bonds formed?
IONIC BONDS are formed when one or more electrons is fully TRANSFERRED between atoms. Ionic bonding is between METALS and NON- METALS.
In ionic bonding what do metals do?
Metal atoms LOSE electrons to form positive ions (CATIONS).
In ionic bonding what do non-metals do?
Non- metal atoms GAIN electrons to form negative ions (ANIONS).
How does an ionic bond form?
Formation of an ionic bond causes a decrease in what? Compared to what?
The positive and negative ions ATTRACT each other, electrostatic interaction, to give an ionic bond.
DECREASE in energy compared to the two isolated atoms.
Properties of an ionic bond:
Formed due to ELECTROSTATIC ATTRACTION between OPPOSITELY CHARGED IONS.
NON- DIRECTIONAL which means the strength of interaction between two ions depends upon distance not the direction.
Ionic compounds DISSOLVE and
disassociate in POLAR SOLVENTS.
Bonds break when substance is MELTED.
Ionic compounds have NO OVERALL CHARGE.
How does an ionic compound dissolve and disassociate in polar solvents?
The bond is broken, and separated ions are surrounded by solvent molecules and interact with solute ions/ molecules.
The bond is broken between oppositely charged ions since the negative ion is attracted to the slightly positive water and the positive ion is attracted to the slightly negative oxygen. If the attraction between the ion and the H/O is strong enough the bond will break.
Features of an ionic bond:
METAL and NON-METAL
DISSOLVES easily in WATER and other polar solvents.
CONDUCTS ELECTRICITY when MOLTEN and in SOLUTION.
Form CRYSTALLINE SOLIDS with HIGH melting temperatures.
How is an ionic lattice formed? What pattern does it repeat?
OPPOSITELY CHARGE IONS attracted to each other which results in a GIANT IONIC LATTICE which is a repeating 3d pattern of ANIONS and CATIONS in a SOLID state.
What is Lattice Energy defined as?
The LATTICE ENERGY is defined as the enthalpy of formation (energy change) of forming one mole of the ionic solid from its gaseous ions- measuring bond strength.
Factors favouring an ionic bond:
Forming a Cation and Forming an Anion. Explain each answer.
Forming a Cation- Low ionisation energy of a metal (Lose electrons easily).
Forming an Anion-
High electron affinity/ electronegativity of a non- metal (Gain electrons easily).
Small size of non- metal (Stronger attraction to electrons because of less shielding).
Low charge of anion (Greater attraction to electrons so easier to add electrons).
Other factors which favour an ionic bond forming:
Large electronegativity difference between combining atoms. High lattice energy of ionic compound (More energy required to break the bonds so there is a strong attraction between ions).
What is polarisation?
The DISORTION of the ELECTRON CLOUD in an atom.
What is polarising power?
The ability to distort electron cloud of another ion.
What atoms have a higher polarising power?
Smaller the ion and higher charge.
Who has more polarising power cations or anions? Why?
Cations are smaller than anions so have a more polarising power whereas anions tend to be polarised.
What atoms have higher polarisability?
The larger an atom and the more electrons the atom has the higher the POLARISABILITY.
What shape is an ideal ionic compound?
Completely SEPERATE and are SPHERICAL ions.
What are the shape of ions and what character do they have if they are polarised?
NON- SPHERICAL ions and COVALENT CHARACTER in bonds
When will an ionic compound have some covalent character?
CATION is SMALL and/ or has a HIGH CHARGE which is highly polarising.
ANION is LARGE and/ or has a HIGH CHARGE which is highly polarising.
What are Polyatomic ions?
Ions which are made up of MORE THAN ONE ION.
What is the bonding in polyatomic ions?
Bonding between atoms in polyatomic ions is COVALENT.
What is a key feature of a polyatomic ion which allows them to get involved in ionic bonding?
Number of electrons in a polyatomic ion means the group has an OVERALL CHARGE so can get involved in ionic bonding.
How do you name an ionic compound?
- First word is cation and usually the parent name.
- Oxidation state of metal may sometimes be given in name.
- The second word is the ANION. If the ion is polyatomic then the name of the polyatomic ion is used. If the second ion is an element then the end of the element is change to -ide.
How are covalent bonds important?
Used in ORGANIC COMPOUNDS which are the building blocks of life.
Determines the SHAPE of molecules which determines interactions between proteins and drugs.
Causes permanent ENZYME INHIBITION.
Determines POLARITY which determines INTERMOLECULAR FORCES so the molecules properties, solubility and receptor interactions.
What are covalent bonds?
ELECTRON PAIRS that are SHARED by both participating atoms.
Why do atoms share 1,2 or 3 electron pairs?
Want to have the same electronic configuration as a noble gas to be stable.
Features of Covalent bonding:
Covalent bonds are a DIRECTIONAL BOND which means a distortion of the electrons are towards an atom.
Covalent bonding is between NON- METALS.
Covalent bonds are formed through SHARED electrons and ELECTROSTATIC ATTRACTION between oppositely charged nuclei and electrons. This attraction forms a covalent bond.
What happens to the number of orbitals when atoms interact to form molecules?
What orbitals do electrons fill from first?
The number of orbitals stays the same for example 2 x 1s orbitals = 2 molecular orbitals.
The orbital with the lowest energy.
What combinations are molecular orbitals?
LINEAR (on the same plain).