TOPIC 2 — BONDING AND THE STRUCTURE Flashcards
CHEMISTRY A-LEVEL EDEXCEL
What are ions?
Ions are charged particles. Ions are formed when electrons are transferred from one atom to another.
What are cations and anions?
Cations are positively charged ions. Anions are negatively charged ions.
What is an ionic bond?
An ionic bond is the strong electrostatic attraction between two oppositely charged particles. The stronger the electrostatic attraction the stronger the ionic bond.
How do ionic charges affect the strength of an ionic bond?
The greater the charge on an ion, the stronger the ionic bond, and therefore the higher the melting/boiling point.
How do ionic radii affect the strength of an ionic bond?
Smaller ions pack closer together than larger ions. Electrostatic attraction gets weaker with distance, so small, closely packed ions have stronger ionic bonding than larger ions. Ionic compounds with small closely packed ions have higher melting and boiling points than ionic compounds made of large ions.
What happens to the ionic radius as you go down a group?
The ionic radius increases as the atomic radius increases. This is because extra electron shells are added.
What are isoelectronic ions?
Isoelectronic ions are ions of different atoms with the same number of electrons.
What happens to the ionic radius of isoelectronic ions as the atomic number increases?
The ionic radius of a set of isoelectronic ions decreases as the atomic number increases.
What happens to the ionic radius as you go across a period?
As you go across a period the number of electrons stays the same but the number of protons increases. Meaning that the electrons are attracted to the nucleus more strongly, pulling them in, so the ionic radius decreases.
How do ionic compounds form giant ionic lattice structures?
Giant ionic lattices form because each ion is electrically attracted in all directions to ions of the opposite charge. In sodium chloride, the Na+ and Cl- ions are packed together alternately in a lattice. Sodium chloride lattice is cubed shape — different ionic compounds have different shaped structures.
What evidence is provided by the physical properties of ionic compounds?
They have high melting points — ions are held together by a strong attraction. Positive and negative ions are strongly attracted, so the model fits the evidence.
They are often soluble in water but not in non-polar solvents — Charged particles. Ions are pulled apart by polar molecules like water, but not by non-polar molecules. Model of ionic structures fits this evidence.
Ionic compounds conduct electricity only when molten or dissolved — Ions which are in a fixed position by strong ionic bonds in a solid, but are free to move as a liquid or solution.
Ionic compounds can’t be shaped — Repulsion between these ions would be very strong, so ionic compounds are brittle (break when stretched or hammered). Supports lattice model.
What is the evidence for the presence of charged particles?
The migration of Ions — When you electrolyse a green solution of copper(II) chromate(VI) on a piece of wet paper, the filter paper turns blue at the cathode (negative electrode) and yellow at the anode (positive electrode).
Copper(II) ions are blue in solution and chromate(VI) ions are yellow. Copper(II) chromate(VI) solution is green because it contains both ions. When a current is passed the positive ions move to the cathode and the negative ions move to the anode.
What holds atoms in molecules together?
Molecules are formed when 2 or more atoms bond together, and are held by covalent bonds.
What is a covalent bond?
A covalent bond is the strong electrostatic attraction between the two positive nuclei and the shared electrons in the bond.
How is electronegativity usually measured?
Electronegativity is usually measured using the Pauling scale. The higher the Electronegativity value, the more electronegative the element. Fluorine is the most electronegative element— Its given a 4.0 on the Pauling scale. Oxygen, chlorine and nitrogen are also very electronegative.
What is the least electronegative value?
The least electronegative elements are have electronegative values of around 0.7.
What happens to electronegativity as you go across a period and up a group?
Electronegativity increases as you go across a period and up a group. Because more electronegative elements face higher nuclear charges and and smaller atomic radii.
