Atomic Structure Flashcards
What is the basic structure of an atom?
The basic structure of an atom is a positively charged nucleus composed of both protons and neutrons surrounded by negatively
charged electrons.
where is most of the mass concentrated in an atom?
the nucleus
Explain how electrons are arranged in an atom:
The electrons are arranged at different distances from the nucleus (different energy levels). The electron arrangements may change
with the absorption of electromagnetic radiation (move further from the nucleus; a higher energy level) or by the emission of
electromagnetic radiation (move closer to the nucleus; a lower energy level).
Explain the relationship between electrons and protons.
In an atom the number of electrons is equal to the number of protons in the nucleus. Atoms have no overall electrical charge.
How is atomic number determined?
All atoms of a particular element have the same number of protons.
The number of protons in an atom of an element is called its atomic number.
How is the mass number determined?
The total number of protons and neutrons in an atom is called its mass number.
What are isotopes?
Atoms of the same element can have different numbers of neutrons; these atoms are called isotopes of that element
How are positive ions formed?
Atoms turn into positive ions if they lose one or more outer electron(s).
What were atoms thought to like before electrons were discovered?
Before the discovery of the electron, atoms were thought to be tiny spheres that could not be divided.
What did the discovery of the electron lead to?
The discovery of the electron led to the plum pudding model of the atom. The plum pudding model suggested that the atom is a ball of
positive charge with negative electrons embedded in it.
How did Neils Bohr adapt the Nuclear model
Niels Bohr adapted the nuclear model by suggesting that electrons orbit the nucleus at specific distances. The theoretical calculations
of Bohr agreed with experimental observations.
Later experiments led to the idea that the positive charge of any nucleus could be subdivided into a whole number of smaller particles, each particle having the same amount of positive charge. The name proton was given to these particles.
What did James Chadwick discover?
the existence of neutrons within the nucleus.
What is radioactive decay?
Some atomic nuclei are unstable. The nucleus gives out radiation as it changes to become more stable. This is a random process
called radioactive decay.
What is activity in terms of nuclear radiation?
Activity is the rate at which a source of unstable nuclei decays.
Activity is measured in becquerel (Bq)
What is count-rate
Count-rate is the number of decays recorded each second by a detector (eg Geiger-Muller tube).
what can the nuclear radiation emit?
- an alpha particle (α) – this consists of two neutrons and two protons, it is the same as a helium nucleus
- a beta particle (β) – a high speed electron ejected from the nucleus as a neutron turns into a proton
- a gamma ray (γ) – electromagnetic radiation from the nucleus
- a neutron (n)
Radio decay is random
What is the half-life of a radioactive isotope?
The half-life of a radioactive isotope is the time it takes for the number of nuclei of the isotope in a sample to halve, or the time it takes for the count rate (or activity) from a sample containing the
isotope to fall to half its initial level.
What is radioactive contamination?
Radioactive contamination is the unwanted presence of materials containing radioactive atoms on other materials. The hazard from
contamination is due to the decay of the contaminating atoms. The type of radiation emitted affects the level of hazard.
What is irridiation?
Irradiation is the process of exposing an object to nuclear radiation. The irradiated object does not become radioactive.
