CHAPTER 2: ATOMS, IONS AND COMPOUNDS Flashcards
What is the mass of a proton, neutron and electron?
Proton = 1 Neutron = 1 Electron = 1/1836
What is the definition of an isotope?
Atoms of the same element with different numbers of neutrons, and different masses
Why do isotopes have no effect on chemical reactions?
Because neutrons do not have an effect on chemical reactions, the transfer and sharing of electrons does. However, higher-mass isotopes will have a higher boiling and melting point, and density.
What is an ion?
Charged particles that is formed when an atom loses or gains electrons
What is a cation?
A positive ion, an atom with fewer electrons than protons.
What is an anion?
A negative ion, an atom with more electrons than protons.
What is the definition of 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.
How do you find relative isotopic mass?
Typically, you assume that it is the same as the mass number (protons + neutrons) of the isotope.
What is relative atomic mass?
Relative atomic mass is the weighted mean mass of an atom of an element relative to 1/12th of the mass of an atom of carbon-12.
How do you find relative atomic mass?
Multiply each isotopic mass by its percentage abundance and divide by 100
How is the percentage abundance of an isotope found?
A mass spectrometer.
What is the basic principle of a mass spectrometer?
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 slowly and are more difficult to deflect than lighter ions, so the ions of each isotope separate.
4- The ions are detected on a mass spectrum as a mass-to-charge ratio. Each ion reaching the detector adds to the signal. So, the greater the abundance, the larger the signal.
What is the mass-to-charge ratio?
Relative mass of ion / relative charge on ion
What is the formula for ammonium?
NH4 +
What is the formula for hydroxide?
OH -
What is the formula for nitrate?
NO3 -
What is the formula for nitrite?
NO2 -
What is the formula for hydrogencarbonate?
HCO3 -
What is the formula for mangenate?
MnO4 -
What is the formula for carbonate?
CO3 2-
What is the formula for sulfate?
SO4 2-
What is the formula for sulfite?
SO3 2-
What is the formula for dichromate?
Cr2O7 2-
What is the formula for phosphate?
PO4 3-
What are the diatomic molecules?
H2, N2, O2, F2, Cl2, Br2, I2
What was stated in Dalton’s atomic theory?
● Atoms are tiny particles made of elements
● Atoms cannot be divided
● All the atoms in a element are the same
● Atoms of one element are different to those of other elements
What did Thompson discover about electrons?
● They have a negative charge
● They can be deflected by magnet and electric field
● They have very small mass
Explain the plum pudding model
Atoms are made up of negative electrons moving around in a sea of positive charge
What were Rutherford’s proposal after the gold leaf experiment?
● Most of the mass and positive charge of the atom are in the nucleus
● Electrons orbit the nucleus
● Most of atom’s volume is the space between the nucleus and the electrons
● Overall positive and negative charges must balance
Explain the current model of the atom
● Protons and neutrons are found in the nucleus
● Electrons orbit in shells
● Nucleus is tiny compared to the total volume of atom
● Most of atom’s mass is in the nucleus
● Most of the atom is empty space between the nucleus and the electrons
What two assumptions are made when calculating mass number?
Contribution of the electron is neglected
Mass of both proton and neutron is taken as 1.0 u
What are the uses of mass spectrometry?
● Identify unknown compounds
● Find relative abundance of each isotope of an element
● Determine structural information
Which are the 4 elements that don’t tend to form ions and why?
The elements are beryllium, boron, carbon and silicon as they require a lot of energy to transfer outer shell electrons
What is an empirical formula?
Simplest whole number ratio of atoms of each element present in a compound
How to calculate empirical formula?
● Divide the amount of each element by its molar mass
● Divide the answers by the smallest value obtained
● If there is a decimal, divide by a suitable number to make it into a whole number