Atomic Structure and Isotopes Flashcards
What is an Ion?
A negatively/positively charged atom or group of atoms, where the number of electrons is different from the number of protons
What is the unit of atomic mass?
unified atomic mass unit ( u )
What is the relative isotopic mass?
The mass of an isotope compared with 1/12th of the mass of an atom of carbon 12
What are 2 assumptions we make when calculating the relative isotopic mass?
- ignore the contribution of electrons within atom
- we take the mass of both protons and neutrons to be exactly 1u
What is relative atomic mass?
The weighted mean mass of an atom of an element compared with 1/12th of the mass of an atom of carbon 12
What is relative molecular mass?
The weighted mean mass of a molecule compared with 1/12th of the mass of an atom of carbon 12
What is relative formula mass? ( This is basically the relative molecular mass of ionic compounds as ionic compounds dont have molecules)
The weighted mean mass of a formula unit compared with 1/12 the of the mass of an atom of carbon 12.
Polyatomic ions
- hydroxide
- nitrate
- carbonate
- sulfate
- ammonium
- phosphate
- hydrogencarbonate
- manganate (VII)
- dichromate
- sulfite
- nitrite
OH-
NO3-
CO3, 2-
SO4, 2-
NH4+
PO4, 3-
HCO3-
MNO4-
Cr2O7, 2-
SO3, 2-
NO2, -
What is the empirical formula?
Simplest whole number ratio of atoms in a compound per element
Why do isotopes have similar chemical properties?
Isotopes of the same element display the same chemical characteristics
This is because they have the same number of electrons in their outer shells
Electrons take part in chemical reactions and therefore determine the chemistry of an atom
What are the differences between isotopes?
The only difference between isotopes is the number of neutrons
Since these are neutral subatomic particles, they only add mass to the atom
As a result of this, isotopes have different physical properties such as small differences in their mass and density
Define atomic number
the number of protons in an atoms nucleus
Define mass number
The number of protons and neutrons in an atoms nucleus
What is the relative mass for a proton and neutron?
1
What is the relative mass for an electron?
1/1836
Define Isotope
Atoms of the same element with different numbers of neutrons and different masses but the same number of protons.
Whats the formula to calculate relative atomic mass?
isotope mass x isotope abundance / 100.
if there are more than 1 isotopes we add them up and then divide.
What is the structural difference between 2H and H2?
H2 is molecular hydrogen. It is bonded together by one single bond. Whereas, 2H denotes two moles of elemental hydrogen
Iron (III) chloride vs Iron (II) chloride
What do the roman numerals tell us about this compound?
The charge i.e Iron (III) chloride has a 3+ charge but Iron (II) chloride has a 2+ charge
When forming an ionic compound by combining ions, what must occur for the ionic compound to form?
We must cancel out the charges
What is molecular formula?
The actual number of atoms (or ions) in a compound
How do we find the empirical formula?
1) find number of moles by doing mass / mr.
2) divide each result by the smallest result to obtain the ratio for the empirical formula
How do we find the molecular formula?
Method 1: Mr (compound) / Mr (empirical) = x
Then do x multiplied by the empirical formula
OR:
Method 2: Do the mass of each element divided by 100 and then multiplied individually by the mr of the compound. Then divide the answers by the smallest answer from the previous step to get the molecular formula
Method 1:
Q) Chemical Analysis of a compound gave the percentage composition by mass whereby:
C= 40.0%
H= 6.67%
O= 53.33%
The relative molecular mass is 180. What is the molecular formula of this compound?
Method 1:
moles of C = 40/12= 3.33 /3.33= 1
moles of H= 6.67/1= 6.67 /3.33= 2
moles of O= 53.33/16= 3.33 /3.33= 1
Then divide each answer by the smallest (3.33)
This gives us the ratio of the empirical formula= CH2O
Mr of compound/ mr of empirical = 180/ (16+12+2)= 180/30 = 6
Now we do: 6 x CH20= C6H12O6
Method 2
Q) Chemical Analysis of a compound gave the percentage composition by mass whereby:
C= 40.0%
H= 6.67%
O= 53.33%
The relative molecular mass is 180. What is the molecular formula of this compound?
C= 40/100 x 180 = 72
H= 6.67/100 x 180 = 12
O= 53.33/100 x 180 = 96
Divide by atomic mass
C= 72/12 = 6
H= 12/1 = 12
O= 96/16 = 6
Hence answer is C6H12O6
What is an atom?
All matter is composed of atoms, which are the smallest parts of an element that can take place in chemical reactions
Why is the mass of an atom concentrated at the nucleus?
The nucleus contains the heaviest subatomic particles (the neutral neutrons and positive protons)
What holds the atom together?
The electrostatic attraction between the positive nucleus and negatively charged electrons orbiting around it.
When can an element have different numbers of protons and electrons?
If its an ION
ons have a different number of electrons to their atomic number depending on their charge
A positively charged ion, or cation, has lost electrons and therefore has fewer electrons than protons
A negatively charged ion, or anion, has gained electrons and therefore has more electrons than protons
Whats the fixed mass for carbon- 12?
fixed as exactly 12 atomic mass units / 12υ
