topic 1 Flashcards
what did john dalton think
atoms are solid spheres
different spheres made up different elements
what did J J Thomson conclude
atoms are not solid spheres
charge and mass shows atoms must contain smaller, negatively charged particles
what is plum pudding model
ball of positive charge with electrons stuck in it
Why did plum pudding change and what did it change to
A small number of positively charged particles deflected backwards so the plum pudding model couldn’t be right as they should’ve all went through due to attraction to electrons
So they made the nuclear model of the atom where there’s a positively charged nucleus at the centre
How did mendeleev arrange elements
Sorted elements into groups based on properties
Put elements in order of atomic mass
However some order was wrong as atomic mass differed due to presence of isotopes
He used properties of other elements to predict gaps where undiscovered elements would be
What is ionic bonding
when a metal and a non metal react together and the metal atom donates its electron to the non metal
properties of ionic compounds
high melting points
high boiling points
due to strong bonds between ions
lots of energy needed to overcome these bonds
ionic compound structure
regular lattice
strong electrostatic forces between oppositely charged ions in all directions
why are 2D models bad
Don’t show the shape or size
Why are dot and cross diagrams bad
No size or how arranged
Why 3D Models bad of atoms
Only show outer layer
Why is ball and stick models bad
Make it look like there are big gaps between the atoms when it’s actually where the electron clouds interact
Not to scale
What’s a covalent bond
Strong bond when a pair of electrons is shared between two atoms
Simple molecular substances made up of a few atoms made by covalent bonds
Properties of simple molecular substances
intermolecular forces are very weak
low melting boiling point
don’t conduct electricity because they aren’t charged so there are no free electrons to move
giant covalent structure properties
high melting and boiling points
strong covalent bonds need lots of energy to break down
don’t conduct electricity due to no charge EXCEPT GRAPHITE!!
not soluble in water
