Atomic structure Flashcards
What are all things made of?
Atoms.
What does an atom consist of?
A small nucleus containing protons and neutrons, with electrons orbiting it.
Where is most of the mass concentrated in an atom?
The nucleus.
What is the diameter of an atom in standard form (m)?
1 x 10^-10m
What is the diameter of a nucleus in standard form (m)?
1 x 10^-14m
How are electrons arranged in an atom?
- At different distances from the nucleus (call them energy levels for physics, shells for chemistry).
- The further away from the nucleus, the higher the energy level is.
What is electromagnetic radiation?
A group of waves which carry energy e.g. light.
What happens if an electron absorbs an electromagnetic wave?
It will move further from the nucleus to a higher energy level.
What can electrons with extra energy do?
Release an electromagnetic wave and fall back to a lower energy level.
What do all atoms of a particular element share?
The same number of protons.
What is the atomic number?
Number of protons in a nucleus.
What is the mass number?
The total number of protons and neutrons in a nucleus.
What are isotopes?
Atoms that have the same number of protons but a different number of neutrons.
Why are most atoms neutral?
- Most of them have the same number of protons and electrons.
- As protons have a charge of +1 and electrons have a charge of -1, these balance out to make the atom neutral/uncharged.
What happens when an atom has a full outer shell?
It becomes stable.
What happens when metals react with other elements?
- They have a few electrons in their outer shell that they lose to become stable.
- The net charge of the atom becomes positive.
- It becomes a cation (positive ion).
What happens when non-metals react with other elements?
- They have almost full outer shells, so they gain electrons to become stable.
- The net charge of the atom becomes negative.
- It becomes an anion (negative ion).
What is an ion?
- A charged atom.
- Negative = anion.
- Positive = cation.
What is charge?
- A physical property of matter.
- Particles can be positively or negatively charged.
What is an electrostatic force?
A force that repels like charges and attracts opposite charges together.
What did Thomson discover?
- Tiny, negatively charged particles called electrons.
- He thought that electrons were surrounded by a ball of positive charge.
- This is called the plum pudding model.
What experiment did Geiger and Marsden carry out?
- They bombarded atoms in a thin sheet of gold foil with tiny positive charges called alpha particles.
- They expected the alpha particles to go through.
- Instead, some were deflected at large angles and some even bounced back.
What did Rutherford conclude from Geiger and Marsden’s experiment?
There is a small, positive nucleus in an atom’s centre containing most of the mass, the rest of the atom is mostly empty space.
What did Bohr discover?
He did calculations to find out that electrons orbit the nucleus at specific distances.
What did various scientists discover after Bohr’s calculations?
Later experiments showed the nucleus could be divided into smaller positively charged particles called protons.
What did Chadwick discover?
Uncharged particles called neutrons.
What conclusions were drawn from Geiger, Marsden and Rutherford’s experiment?
- Most alpha particles went straight through the gold foil = the atom is mostly empty space.
- Some were deflected at large angles = the nucleus of the atom is positive.
- Some bounced backwards = there is a very small nucleus containing most of the mass.
What is are isotopes?
Atoms with the same number of protons but a different number of neutrons.
What are unstable isotopes called?
Radioactive.
What is radioactive decay?
A random process when the nucleus of an unstable isotope gives out radiation as it changes to become more stable.
What is activity (in radioactive terms)?
The rate in which a radioactive source decays (no. of decays per second). It is measured in becquerel (Bq).
How do we measure radioactivity?
- We use a device called a Geiger-Muller tube.
- Count rate is the no. of decays recorded each second by the detector.
- It does not equal activity as the detector can’t record every single decay as it cannot surround the source on all sides.
How many types of radiation are there?
Four; alpha particle, beta particle, gamma wave and neutron.
What is an alpha particle made of?
2 protons and 2 neutrons (a helium nucleus).
What is a beta particle made of?
A neutron that turns into a proton and releases a fast moving electron.
What is a gamma wave made of?
An electromagnetic wave.
What is the range in air for each type of radiation (excluding the neutron)?
- Alpha particle: < 5cm
- Beta particle: ~ 1m
- Gamma wave: > 1km
What is the ionising ability for each type of radiation (excluding the neutron)?
- Alpha particle: high
- Beta particle: medium
- Gamma wave: low
What is each type of radiation stopped by (excluding the neutron)?
- Alpha particle: paper
- Beta particle: thin aluminium
- Gamma wave: thick lead
What is ionising ability?
How likely the radiation is to remove electrons from the atoms they collide with.
What can the emission of nuclear radiation change?
The mass or atomic number of an atom.
How are alpha particles written as in an equation?
He (mass number = 4, atomic number = 2) like helium.
How are beta particles written as in an equation?
e (mass number = 0, atomic number =-1) like an electron.
How is alpha decay written as an equation?
atom -> new atom (mass decreased by 4, atomic by 2) + He
How is beta decay written as an equation?
atom -> new atom (atomic increased by 1) + e
Why does gamma decay not require an equation?
It does not change the mass of atomic number of an atom.
What is the half-life of a radioactive isotope?
The time it takes for the number of nuclei in a sample of the isotope to halve.
What is irradiation?
When radiation from a source hits an object. This does not make the object radioactive.
What does radiation do to matter?
- It ionises it.
- This can damage tissues leading to systems in the body stopping working (radiation sickness).
- It also may cause cells to replicate quickly or mutate; this is cancer.
What is contamination?
- When radioactive substances are mixed with other substances.
- This is very dangerous as the contaminating atoms will continue to decay.
What are the safety precautions for handling radioactive isotopes?
- Minimising exposure time.
- Using lead screens.
- Storing sources in lead containers.
- Wearing disposable clothes.
- Increasing the distance from the source using tongs or robotic arms.
What are the medical uses for radioactive isotopes?
They are used in hospitals for x-rays but the dose for patients should be kept to a minimum.
