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
What kind of nuclear reaction gives the Sun its shine?
nuclear fusion
What are cosmic rays?
high-energy rays coming to Earth from space
What is quantum mechanics?
The system of physical laws that governs the behaviour of elementary particles
How does a particle spin?
Either in integer or half-integer values
What is a boson?
A full spin of a particle
What is a fermion?
A half spin of a particle
What is the charge of an up spin?
positive
What is the charge of a down spin?
Negative
What is the primary duty of bosons?
To carry force and energy
What is the primary duty of fermions?
To make up matter
How are bosons grouped?
Arbitrarily
What is the exclusion principle? (2)
It explains why only one of 2 electrons are able to occupy the closest orbital radius; one has spin up energy one has spin down energy
Fermions cannot interact with each there since they must have distinct quantum states
What is an antiparticle?
Mirror image of the particle except it just has the opposite charge to the other
What is the antiparticle to an electron called?
A positron
What happens when a particle collides with its antiparticle?
Both are converted to pure energy in the form of gamma rays
What is the antiparticle of a photon?
A photon is its own antiparticle
What are the 4 fundamental forces of nature?
- electromagnetic force
- gravity
- strong interaction
- weak interaction
What is strong interaction
the force that holds nucleons together
What is weak interaction
force that mediates nuclear reactions such as fission and beta decay
When do the 4 fundamental forces arise?
When there is an exchange of carrier bosons (gauge bosons)
Why is gravity and electromagnetic force unlimited?
Their bosons are massless
What is electromagnetic force?
The force that exists between charged particles
What is ‘work’?
the exertion of a force to cause a displacement
what is ‘energy’?
the capacity to do ‘work’
what is heat?
the aggregate energy of the particles
what is thermodynamics?
the study of energy in general, heat in particular
what is temperature?
the mean random kinetic energy of th particles
what is the first law of thermodynamics?
the law of conservation of energy
what is the second law of thermodynamics?
in any process, the overall entropy increases or at best remains the same
what is the 3rd law of thermodynamics?
absolute zero may never be attained, but only approached arbitrarily and closely
what is the amplitude of a wave?
the wave’s maximum displacement
what is the crest of a wave?
the highest point of the wave
what is the trough of a wave?
the lowest point of a wave
when does constructive interference occur
when 2 troughs or 2 crests meet
this causes a greater displacement than is present in either wave
when does a destructive interference occur?
when a crest and a trough meet
this means that net displacement is reduced or even cancelled
What is the Doppler effect?
The sound of something fast approaching has its pitch raised as it gets closer to you
What is a blueshift (Doppler effect)
An approaching object shifts the light waves so that they bunch up and are thus shifted towards higher frequencies
What is a redshift (Doppler effect)
a receding object shifts the waves so that they are of lower frequencies
What can the Doppler effect tell us about stars, nebulae and nearby galaxies?
how fast the object is moving towards/away from the earth
What can we conclude if there is a measure of a redshift and a blueshift?
the object is rotating
What is the relationship of speeds of electromagnetic waves in a vacuum?
all of the waves travel at the same speed
When does thermal radiation occur?
in any object with a temperature greater than absolute zero
What was Planck’s breakthrough?
he made the assumption that radiation could only be absorbed or emitted in specific, discrete places
How can we determine the mass of celestial objects?
By the gravitational force it exerts on other objects
what are spiral galaxies?
great disks of stars
what are elliptical galaxies?
stars clustered in elliptical pattern
what are irregular galaxies?
stars in a random order
What is a cluster of a cluster of galaxies called?
a supercluster
