Atomic structure Flashcards
Define the term proton
A positively charged particle found in the nucleus of an atom
Define the term neutron
A neutral particle found in the nucleus of an atom
Define the term electron
A negatively charged particle that orbits the nucleus of an atom.
Define the term atom
The smallest unit of an element, contains neutron(s) and proton(s) in the nucleus and electron(s) in outer shells. It always has a neutral charge
Define the term ion
An ion will be positive when an electron is removed from an atom or negative if an electron is added
Define the term atomic number
The atomic number tells us how many protons there are in an atom, it is sometimes called the Z number. It defines an elements postion on the periodic table
Define the term mass number
The mass number tells us the total of protons and neutrons in an atom it is sometimes called the A number
Define the term element
A substance which is made from only one type of atom
Define the term compound
A substance which is made from more than one type of atom.
Some elements have different isotopes, what does this mean?
The name of an element is defined by its atomic number ie the number of protons in the nucleus but some elements have different numbers of neutrons and therefore different mass numbers, they are called isotope of the element.
Eg Sodium has two isotopes Na23 and Na 24, both have 11 protons but one has 12 neutrons and the other 13.
Who first suggested the idea of atoms
Democritus a Greek philosopher (460-370BC)
Who discovered that electrons were emitted from the surface of hot metal and when was it.
J J Thompson in 1897, he showed that they were negatively charged and less massive than an atom.
What model did J J Thompson suggest for the atom.
The plum pudding model with electrons dotted around inside a positively charged sphere
What is an alpha particle?
It is a positively charged helium ion He2+
Describe the gold foil experiment carried out by Geiger and Marsden in 1909
They directed a beam of alpha (He2+) particles which travel very quickly through a thin sheet of gold . They expected all of the particles to pass through but a small number were deflected and bounced back.
How did Rutherford explain the results of the gold foil experiment
He suggested that the deflection of the alpha particle was due to an electrostatic charge between the particle and a very small charged nucleus, he also said the nucleus could be massive.. He said that the nucleus may be either positively or negatively charged. A positive charged nucleus would deflect the positively charged alpha particle away whereas a negatively charged one would pull the particle toward and around it.
How is the gold foil experiment explained nowadays.
The diameter of the nucleus of an atom is tiny in comparison to the atom 1:20000. The nucleus is positively charged. Most of the alpha particles pass through the gold atom. A few hit the nucleus and were deflected back as the positive charges repelled each other. Some came near the nucleus and were deflected slightly. .
Who discovered that there are neutrons in the nucleus of an atom.
James Chadwick 1932
Describe the model of the atom suggested by Neils Bohr in 1913
He suggested that electrons orbit the nucleus at specific distances.
Explain the positive and negative points of Bohr’s 1913 explanation of the model of the nucleus
Positive
1. It explains why hydrogen emits particular wavelengths of electromagnetic radiation
Negative
It does not allow a full explanation of the behaviour of atoms in larger atoms
Describe the discovery of radioactivity
- Discovered by Henry Becquerel
- In 1898
- He left uranium salts next to a photographic plate which was sealed into a black bag.
- When the plate was developed it had been affected as if it had been exposed to light.
- He realised that particles had been emitted from the uranium salts and passed through the bag.
Describe nuclear decay
Most atoms have stable nuclei, some however do not and throw out particles to make themselves more stable. It is a random process and it not affected by other factors such as temperature and chemical reactions. Radium is one element which does this. The name for it is radioactivity.
Identify the four types of radioactive emission.
- Alpha particles
- Beta particles
- Electromagnetic waves (gamma rays)
- Neutrons
Explain the term alpha decay
An alpha particle consists of 2 protons and 2 neutrons. When an alpha particle is emitted from a nucleus it causes the nucleus to change into another with a mass number of 4 less and an atomic number 2 less.
