Topic 1 - Key Concepts in Chemistry Flashcards
John Dalton’s theory about the atom
- Atoms cannot be created, divided or destroyed.
- Atoms of the same element are exactly the same and atoms of different elements are different.
- Atoms join with other atoms to make new substances
What discovery caused Dalton’s model to change?
The discovery of sub-atomic particles
Who discovered the electron?
JJ Thomson
What did JJ Thomson discover?
The electron
How was the electron discovered?
- Thomson experimented with a cathode ray tube.
- The beam moved towards the positively charged plate so he knew that the particles must have a negative charge.
What model was proposed by JJ Thomson?
- Plum pudding model
- Negatively charged electrons scattered through a positively charged metal
Who discovered the Plum Pudding Model?
JJ Thomson
What was the plum pudding model?
Negatively charged electrons scattered through a positively charged metal
Who conducted the gold foil experiment?
JJ Thomson
What was the gold foil experiment?
- JJ Thomson shot a beam of positively charged particles at sheet of gold foil.
- Most particles passed straight through suggesting atoms are mostly empty space.
- A few particles were deflected and a few bounced back showing there must be a tiny, dense, positively charged nucleus.
Rutherford’s model of the atom:
- Mass is concentrated in the central nucleus
- The atom is mostly empty space.
- Electrons travel in random paths around the nucleus
Structure of the atom
- Small central nucleus made up of protons and neutrons.
- Electrons orbit the nucleus in shells.
The radius of the nucleus
1x10^-14 metres. This is 1/10,000 of the atomic radius.
Relative masses of sub-atomic particles
Proton - 1
Neutron - 1
Electron - 1/1840
Relative charges -
Proton: +1
Neutron: 0
Electron: -1
Why do atoms contain equal numbers of protons and electrons?
- Atoms are stable with no overall charge.
- Protons are positively charged and electrons are negatively charged so for charges to balance the number of protons and electrons must be equal.
Where is the mass of an atom concentrated?
In the nucleus
Atomic number represents
Number of protons.
Mass number -
Number of protons + number of neutrons
Fill in the blank:
‘Atoms of the same element have the same number of ______ in the nucleus and this is unique to that element’
Protons
What’s an isotope?
- Isotopes are atoms with the same number of protons (so they are the same element) but a different number of neutrons.
- Isotopes of an element have the same atomic number but different mass numbers.
Exam Question - Boron has the atomic number 5 and the mass number 11. How many protons, electrons and neutrons does Boron have?
5 Protons
6 Neutrons
5 Electrons
Why is relative atomic mass not always whole?
- Different isotopes of the same element have different mass numbers.
- The relative atomic mass is an average of the masses of all these isotopes.
What two values would be required to calculate the relative atomic mass of chlorine?
Mass numbers and relative abundances of all the isotopes of chlorine.
How did Mendeleev arrange the elements in his periodic table?
- Elements arranged with increasing atomic masses.
- Elements with similar properties put into groups (due to periodic trends in chemical properties).
- Switched the position of some elements.
- Gaps left for undiscovered elements.
How was Mendeleev able to predict the properties of new elements?
- Mendeleev left gaps in his periodic table.
- He used the properties of elements next to these gaps to predict the properties of undiscovered elements.
Mendeleev’s table lacked some amount of accuracy in the way he’d ordered his elements. Why was this?
- Isotopes were poorly understood at the time.
- Protons and neutrons had not yet been discovered.
How are elements arranged in the modern periodic table?
In order of increasing atomic number
Fill in the blank: ‘Elements in the same group (column) have similar _______ ______’
Chemical properties
Why do elements in the same column have similar chemical properties?
- Same number of outer shell electrons.
- Number of outer shell electrons determines how an atom reacts.
What does the period (row) number tell you about all the elements in that period?
- Elements in the same period have the same number of electron shells.
- e.g. all elements in period 4 have 4 shells of electrons.
What does group (column) number tell you about all the elements in that group?
- All elements in the same group have the same number of outer electrons.
- e.g. all elements in group 2 have 2 electrons in their outer shell
Where on the periodic table are metals?
Left hand side
What determines whether something is metal or non-metal?
Atomic structures of elements
What is the maximum number of electrons allowed in each of the first 3 shells?
1st Shell - 2
2nd Shell - 8
3rd Shell - 8
When are atoms most stable?
When they have full electron shells
The atomic number of Na is 11. What is the electron configuration of Na?
2, 8, 1
How is the electron configuration of an element related to its position in the periodic table?
- The number of shells is the period.
- The number of electrons in the outer shells is the group.
- The total number of electrons is the atomic number.
What is an ionic bond?
A bond between a metal and non-metal involving the transfer of electrons.