Flashcards in Module 2: Chapter 2 (Atoms, ions and compounds) Deck (31)
Describe the nuclear atom
- atom consists of a nucleus made up of two types of subatomic particle - protons and neutrons
- third subatomic particle is called an electron, arranged outside the nucleus in shells
What is an isotope?
Isotopes are atoms of the same element (same number of protons) with different numbers of neutrons, and therefore different masses
What are the chemical and physical properties of isotopes?
- In chemical reactions isotopes retain the same level of reactivity as they have the same number of electrons in the outer shells -> isotopes of the same element would react in a similar way
- physical properties change with each isotope
What are cations?
Positive ions, have fewer electrons than protons
What are anions?
Negative ions, have more electrons than protons
Discuss the mass of an atom
- The mass of an atom is not exactly the same as the individual masses of the constituent protons, electrons and neutrons
- The strong nuclear force binding the protons and nucleus comes at the expense of a fraction of their mass, mass defect
Why is carbon-12 an important isotope?
- this isotope is the international standard for the measurement of atomic masses
- mass of a carbon-12 isotope is defined as exactly 12 atomic mass units (12u)
- Standard mass for atomic mass is 1U, mass of 1/12th of a carbon-12 isotope
- 1u = approx. mass of proton/neutron
What is relative isotopic mass?
Relative Isotopic mass is the mass of an isotope relative to 1/12th of the mass of an atom of carbon-12
What is relative atomic mass?
Relative atomic mass Ar is the weighted mean mass of an atom of an element relative to 1/12th of the mass of an atom of carbon-12
the weighted mean mass takes into account the percentage abundance and relative isotopic mass of each isotope
How does mass spectrometry work?
- Technique used to experimentally find the percentage abundances
1. a sample is placed in the mass spectrometer
2. the sample is vaporised and then ionised to form positive ions
3. the ions are accelerated, heavier ions move more slowly and are more difficult to deflect than lighter ions, so the ions of each isotope are separated
4. the ions are detected on a mass spectrum as a mass-to-charge ratio m/z, each ion reaching the detector adds to the signal, so the great the abundance the larger the signal
Describe how each atom becomes a simple ion
• Atoms of metals in groups 1,2,3 all lose electrons to form positive ions
• Atoms of non-metals in groups 15,16,17 all gain electrons to form negative ions. These ions can me named adding 'ide' to the stem
State the two ions of hydrogen
What is the ion charge of Zinc?
What is the ion charge of Silver?
What are polyatomic ions?
Polyatomic ions contain atoms of more than one element covalently bonded together
What is the overall charge of an ionic compound?
What are the charges and masses of the subatomic particles?
p+, 1+, 1
n, 0, 1
e-, 1-, 1/1836
What are the state symbols?
(g) = gas (e.g. vapour)
(s) = solid (e.g. precipitate)
(l) = liquid (water)
(aq) = dissolved in water (e.g. solution)
What is the formulae for elements that exist as small molecules?
H2, O2, N2, All group 17 (F2, Cl2,Br2, I2), P4 and S8 (sometimes just written as 'S'
What is the formulae for some common covalent compounds?
H2O, CO2, CO, NH3, NO2, NO, SO2