1. Atomic Structure and the periodic table Flashcards
(16 cards)
What is the definition of an atom?
An atom is the smallest part of an element that can exist.
What is an element?
An element is a substance that contains one type of atom
What is a compound?
A compound is two or more elements (different types of atoms) that are chemically combined.
What is a molecule?
Two or more atoms chemically bonded (can be same or different, e.g both CO2 and O2 are molecules, but O2 is also an element, and CO2 is also a compound)
What is a mixture?
Two or more elements that are not chemically bonded. The chemical properties of each substance in the mixture are unchanged.
What kind of substance is nitrogen?
Nitrogen is both an element and molecule.
Balance these equations:
Ca + O2 → CaO
Na2O + H2O → NaOH
Al + O2 → Al2O3
Na + Cl2 → NaCl
Na2CO3 → Na2O + CO2
K + O2 → K2O
2Ca + O2 → 2CaO
Na2O + H2O → 2NaOH
2Al + 3O2 → 2Al2O3
2Na + Cl2 → 2NaCl
Na2CO3 → Na2O + CO2
4K + O2 → 2K2O
Name the five scientists you’re supposed to know about for the history of the atom, in order (excluding Democritus in 400BC)
- John Dalton
- J.J Thomson
- Ernest Rutherford
- Niels Bohr
- James Chadwick
What did John Dalton think ‘bout the atom?
In the early 1800s, Dalton suggested that atoms were the smallest particle and were indivisible (could not be divided)
What did J.J Thomson have to say about the atom?
In the late 1800s, Thomson found out that atoms are made of positive and negative charges. He discovered that the negative charges are called electrons (but didn’t know the name of protons - just positive charge). He developed the Plum Pudding model.
Therefore atoms CAN be divided.
Describe the plum pudding model.
Ball of positive charge with negatively charged electrons randomly scattered inside it.
What about his homie Ernest Rutherford - what did he do?
Ernest Rutherford was hardcore bromancing with J.J Thomson, so he set out to prove his plum pudding model as correct, so he conducted the alpha particle scattering experiment. He had a gold sheet full of atoms and fired alpha particles (positively charged helium atoms) and expected all of them to go through. However, his zesty dreams were crushed when he found that most of them went through, suggesting that there is empty space in the atom. A few deflected back because it hit a high area of positive charge (nucleus). This also meant that the mass was concentrated at the centre of the atom. Therefore, Ernest Rutherford discovered the nucleus of the atom. Later he discovered the proton, which is positively charged, making the nucleus positively charged. This developed the nuclear model.
Describe the alpha particle scattering experiment.
Thin gold sheet. Alpha particles fired at thin gold sheet. Most went through - meaning that the atom is mostly empty space. A few deflected back, meaning that the particles hit an area of high positive charge, aka the nucleus, as two positive charges repel. The size of a nucleus is like football in a football stadium.
What did Emily’s brethren Niels Bohr have to say about the atom?
In 1913, Bohr published a paper that showed how the electrons don’t move randomly outside the nucleus, but are flying around the atom fitted into shells.
The plum pudding model of the atom was replaced by the nuclear model. The nuclear model was developed after the alpha particle scattering experiment. Compare the plum pudding model and the nuclear model. - Remember for these questions think about what model the examiners are referring to - is it Rutherford’s nuclear model, Bohr’s nuclear model, or Chadwick/today’s atomic model?
Similarities:
Both contain positive charge
Both contain negative charge (electrons)
Neither have neutrons
Plum pudding model:
Ball of positive charge (spread throughout)
Electrons spread throughout and are embedded inside the ball of positive charge
No empty space in the atom
Mass spread throughout
Nuclear model:
Positive charge concentrated at the centre
Electrons outside the nucleus
Most of the atom is empty space
Mass concentrated at the centre of the atom
What did the newbie/latecomer James Chadwick have to say about the atom?
He discovered the neutron, and the the nucleus not only contained the positive charge but also the neutrons (which is really heavy so it contains most of the atom’s mass). Neutrons have no charge (they’re neutral).
