1. Key Concepts In Chemistry Flashcards
Why has the Dalton model of an atom changed over time?
Because of the discovery of subatomic particles.
What is the structure of an atom?
- Small central nucleus made up of protons and neutrons.
- Electrons orbit (move around) the nucleus in shells.
Relative charge of proton
+1
Relative mass of proton
1
Relative charge of neutron
0
Relative mass of neutron
1
Relative charge of electron
-1
Relative mass of electron
1/2000
Why do atoms contain equal number of protons and electrons?
Atoms are neutral as the charges of a proton is +1 and an electron is -1, therefore the amount of protons = amount of electrons, so the charges cancel each other out.
TRUE OR FALSE: The nucleus of an atom is very small compared to the overall size of an atom.
True
Where is the most mass of an atom concentrated?
In the nucleus.
What is mass number?
Number of protons + neutrons
TRUE OR FALSE: The atoms of the same element have different number of protons in the nucleus.
False - they have the same number of protons and this number is unique to that element.
What are isotopes?
Isotopes are atoms with the same number of protons (so they are the same element)
but a different number of neutrons.
Isotopes of an element have the same atomic number but different mass numbers.
What is atomic number?
Number of protons (= number of electrons if it’s an atom, because atoms are neutral)
Explain how the existence of isotopes results in relative atomic masses of some elements not being whole numbers
- The relative atomic mass is calculated using the abundance of different isotopes and because it is an average it can lead to the relative atomic mass not being a whole number
How to calculate relative atomic mass
R.A.M = (mass of isotope-A x % of isotope-A) + (mass of isotope-B x % of isotope-B) / 100
A sample of chlorine gas is a mixture of 2 isotopes, chlorine-35 and chlorine-37. These isotopes occur in specific proportions in the sample i.e. 75% chlorine-35 and 25% chlorine-37. Calculate the R.A.M of chlorine in the sample.
R.A.M = (35 x 75) + (37 x 25) / 100
R.A.M = 3550/100
R.A.M = 35.5
How did Mendeleev arrange the elements, known at that time, in a periodic table?
- Elements arranged with increasing atomic masses.
- Elements with similar properties put into groups (due to periodic trends in chemical properties).
- Switched the position of some elements.
- Gaps left for undiscovered elements.
How was Mendeleev able to predict the properties of new elements?
- Mendeleev left gaps in his periodic table.
- He used the properties of elements next to these gaps to predict the properties of undiscovered elements.
Mendeleev’s table lacked some amount of accuracy in the way he’d ordered his
elements. Why was this?
- Isotopes were poorly understood at the time.
- Protons and neutrons had not yet been discovered.
What are vertical columns called in the periodic table?
Groups
What are horizontal rows called in the periodic table?
Periods
What do elements in the same group have in common?
They have the same amount of electrons in their outer shell, which gives them similar chemical properties. The number of outer shell electrons determines how an atom reacts.
How are elements arranged in the periodic table?
In order of increasing atomic number in rows called periods.
What are metals
Elements that react to form positive ions by losing electrons.
Where in the periodic table are metals found.
To the left and towards the bottom of the periodic table - most elements are metals.
What are non-metals
Elements that react to form negative ions by gaining electrons.
What is electronic configuration of an element and what does it tell us?
Tells you how many electrons are in each shell around the nucleus.
- For example, sodium has 11 electrons: 2 in its most inner shell, then 8, then 1 in its outermost shell. 2.8.1
How does group number relate to electronic configuration?
The group an electron is in tells you how many electrons are in its outermost shell, e.g. group 1 elements have 1 electron in their outer shell.
How does period number relate to electronic configuration?
The period an electron is in tells you which number shell an element’s outermost
electron is found in, e.g. period 3 elements have their outermost electrons in
shell 3.
How are ionic bonds formed?
By the transfer of electrons between atoms to produce cations and anions.
What happens when there is ionic bonding between a metal and a non-metal?
Electrons in the outer shell of the metal atom are transferred.
- Metal atoms lose electrons to become a positively charged ion (cation).
- Non-metal atoms gain electrons to become a negatively charged ion (anion).
How is electron transfer during the formation of an ionic compound represented?
Dot and cross diagram.
What is an ion?
An atom or group of atoms with a positive or negative charge.
How to calculate number of electrons in an ion (as ions have different number of electrons to protons)
- Work out how many electrons an atom of the element would have (same as proton number).
- Work out how many electrons have been gained or lost.
- Calculate number of electrons in atom plus electrons gained or minus electrons lost.
What group are noble gases found?
Group 0
How many electrons will metals in group 1 gain/lose and what type of ions will they form?
Lose 1 electron , form +1 ions
How many electrons will metals in group 2 gain/lose and what type of ions will they form?
Lose 2 electrons , form +2 ions
How many electrons will nonmetals in group 6 gain/lose and what type of ions will they form?
Gain 2 electrons , form 2- ions
How many electrons will nonmetals in group 7 gain/lose and what type of ions will they form?
Gain 1 electron , form 1- ions
What overall charge will an ionic compound have?
An overall charge of 0 because you need to balance out the + and - charges.
Explain the use of the –ide ending in the names of compounds
-ide means the compound contains 2 elements (one is the nonmetal negative ion)
Explain the use of the –ate ending in the names of compounds
-ate means the compound contains at least 3 elements, one of which is oxygen.