Electron Arrangement
What charge does an electron have?
Negative
What does the production of bubbles during a reaction often indicate?
A gas has been produced
What is radioactive decay?
The spontaneous breakdown of an unstable nucleus.
What information does the atomic number tell you?
The number of protons in an atom.
What is an ion?
A charged particle formed when an atom gains or loses electrons.
Where are electrons found in an atom?
In energy levels/shells around the nucleus
If a reaction causes the temperature of the surroundings to increase, what type of energy change has occurred?
Exothermic
What is the name given to the time taken for half of a radioactive sample to decay?
Half-life
An element has an atomic number of 8. What element is it?
Oxygen
What happens to an atom when it gains electrons?
It becomes a negative ion (anion).
How many electrons can the second shell hold for the elements studied at this level?
8
Is colour change enough evidence to suggest a chemical change has occured?
No
Name the three common types of nuclear radiation.
Alpha, beta and gamma
An element has an atomic number of 17. How many protons and electrons does a neutral atom have?
17 protons and 17 electrons.
An atom has 11 protons and 10 electrons. What is its charge?
+1
What is the electron arrangement of oxygen (atomic number 8)?
2, 6
If a reaction causes the surroundings to become colder, what type of energy change has occurred?
Endothermic
A radioactive isotope has a half-life of 10 years. How much remains after 30 years?
12.5%
Element X has atomic number 12. Use the periodic table to identify it and state its electron arrangement.
Magnesium; 2, 8, 2.
What ion is formed when a chlorine atom gains one electron?
Cl⁻
An atom has 2, 8, 8 electrons. Is it likely to be reactive or relatively unreactive? Explain.
Relatively unreactive because its outer shell is full.
A student mixes two substances. There is no colour change, no gas, no precipitate and no measurable temperature change. Does this prove that no chemical reaction occurred?
No. A reaction may have occurred without an obvious observable change; other evidence or testing may be required.
A sample starts with 800 radioactive atoms. How many remain after three half-lives?
100
An unknown element has 3 electron shells and 1 electron in its outer shell. Where would you expect it to be located on the periodic table?
Group 1, Period 3 — Sodium.
Explain why sodium forms Na⁺ rather than Na²⁺.
Na⁺ rather than Na²⁺.Sodium has one outer-shell electron, so it is much easier to lose one electron and achieve a stable arrangement.