Halogens Flashcards
What is a hydrogen halide?
Hydrogen bonded with halogen
Are all of the hydrogen halides strong acids?
No, all are apart from HF. Hydrogen fluoride is a weak acid (doesn’t completely dissociate)
Why is hydrogen fluoride a weak acid?
It has very strong bond energy and even if the bond is broken the ions are so strongly attracted to each other they recombine so the H3O ion is not free
Why does HF not follow the trends of boiling and melting point?
Because it forms hydrogen bonds. These bonds must be broken before it is turned into a liquid or gas, thus needs more heat energy
Why does HF form hydrogen bonds?
Fluorine is very electronegative, thus creates a very polar bond between the h and the f. Also the lone pairs on F are in an extremely small and dense area so another HF atom is sos strongly attracted to this it is like a bond
Do other halogens form hydrogen bonds?
They aren’t electronegative enough to form theses bonds
Bronsted-Lowry definition of an acid
Proton donor
What makes most hydrogen halides strong acids?
They almost completely dissociate and donate hydrogen
Describe the atomic radius trend down group 7
Size increases. Because the number of shells increases which also increases shielding so the outer electrons don’t feel as strong an attraction
What is electronegativity
The ability of the atom to draw electrons towards itself
Describe electronegativity trend down group 7
Electronegativity decreases down the group. Because atoms get bigger so the nucleus is further away attraction is less
What is electron affinity
The energy given off when 1 mole of gaseous atoms gain electrons to form 1 mole of gaseous -1 ions. So she shows attraction between nucleus and incoming electron
Describe electron affinity down group 7
Generally decreases with the exception of F. It generally decreases because atoms get bigger so attraction to nucleus is less. But in the case of fluorine the dense lone pairs can repel incoming electrons
Describe tends of melting and boiling points down group 7
Melting and boiling points increase down the group. This is because the atoms get bigger, meaning the forces of Vander waals forces. It’s harder to break so more heat is needed
What are bond enthalpies?
Known as bond strengths it is the heat needed to break a mole of substance into individual atoms
