Chapter 4 Flashcards
How much of the universe is Helium?
24%
How much of the universe is Hydrogen?
75%
Who began the study of chemistry?
Lavoisier and Priestly
What are combinations of 2 or more atoms called?
Compounds
How was the idea of a charge first discovered?
The ancient Greeks knew that amber, when rubbed with fur, could attract small particles
What is the charge of an electron?
Negative
What was the ‘Plum Pudding Model’?
The idea that electrons actually existed inside of the atom, like the bits of a plum pudding
How was the Plum Pudding Model disproved?
Ernest Rutherford dots alpha particles at a gold sheet and found that they almost always passed through with only slight deflections.
What was Rutherford’s model of the atom?
Tightly packed, positive nucleus with orbiting electrons
What was the Bohr Atom?
Electrons orbited the nucleus at discrete orbits of fixed energy
What happens when an electron changes orbit?
It either emits or takes in energy do make this shift
How can light be characterised?
As discrete particles called photons
How could a transition from one orbit to another be achieved according to Bohr?
The photon could cause the electron to transition to a higher orbit only if it has the exact energy equalled the difference in energy levels
How are the chemical properties of an element determined?
Through the number and arrangement of the electrons
What are inert gases and why are they unique?
They have a full outer shell of electrons and as such will not partake in reactions as much
What is the net electrical charge gained or lost in a chemical reaction called?
an ion
What is a covalent bond?
Where an atom shares electrons
What is an ionic bond?
When a positive and negative compound’s charges attract and form a chemical compound
Why is a positively ionised gas more opaque?
Because the free electrons interact with the light and scatter it
What is an isotope?
Two atoms with the same number of protons but different number of protons
They are still the same element since the number of protons is the same
How was radiation discovered?
Henri Becquerel left a uranium compound on top of some film and it left an image
What are the 3 types of radiation
Alpha particles
Beta particles
Gamma rays
What makes up an alpha particle?
2 protons, 2 neutrons
What makes up a beta particle?
Electrons
What makes a gamma ray?
Essentially rays of light with very high energy
What happens when a nucleus emits an alpha particle?
It transmutes into another element which has 2 fewer protons
What happens when a nucleus emits a beta particle?
It transmutes into an isotope of the same element, which has one more proton and one less neutron
What is a half life?
When half the members of the original nuclei have decayed
What is the significance of a half life?
It can be used to estimate the Galaxy’s age
What is nuclear fission?
When a nucleus splits to form two lighter nuclei. This releases a lot of energy
What is nuclear fusion?
2 nuclei combine to form a heavier element. This also releases a lot of energy