period table and its use

who defined the term element

Robert Boyle

1b) What is an element?

An element is a substance that cannot be split into simpler substances by chemical means

2) Name the scientist shown, who discovered many elements by passing electricity through their compounds

Humphry Davy

3a) Name the scientist shown who proposed the periodic law for arranging elements in the periodic table.

Dmitri Mendeleev

3b) What was the periodic law?

If the elements are arranged in order of increasing atomic weight and elements with similar properties were placed beneath each other in groups, chemical properties repeat at regular intervals

3c) Why did this scientist leave gaps in his periodic table?

For undiscovered elements

3d) How was this scientist able to predict the properties of elements that had not yet been discovered?

Because elements in the same group have similar properties

3e) Why did this scientist reverse the order of some elements? Example: Why did he place Tellurium before Iodine even though Iodine has a smaller atomic weight?

To ensure elements with similar properties were in groups - chemical properties matched better

4a) Name the scientist shown who for the first time did not arrange the periodic table according to atomic weight

Henry Moseley

4b) Outline the contribution of this scientist to the development of the periodic table

Discovered a method for determining no. of protons in the nucleus of an element and arranged elements according to this (atomic number)

4c) What is an advantage to arranging the elements of the periodic table in the order suggested by this scientist?

Elements with similar properties fall naturally into the same groups

5) Give three differences between Mendeleev’s periodic table and the modern periodic table

1. Mendeleev: Arranged by atomic weight; Modern: Arranged by atomic number

2. Mendeleev: Contained gaps for undiscovered elements; Modern: No gaps

3. Mendeleev: Fewer elements (60); Modern: More elements (118)

6a) What is an ion?

An ion is an atom with a charge

6b) How does an atom become a positive ion?

By losing electron(s)

6c) How does an atom become a negative ion?

By gaining electron(s)

6d) What name is given to a positive ion?

Cation

6e) What name is given to a negative ion?

Anion

6f) Define atomic number

Atomic number gives the number of protons in the nucleus of an atom or ion

6g) Define mass number

Mass number gives the TOTAL SUM of protons and neutrons present in the nucleus of an atom or ion

7a) Potassium (K)

i) 19 protons

ii) 20 neutrons

iii) 19 electrons

7b) Chlorine (Cl)

i) 17 protons

ii) 18 neutrons

iii) 17 electrons

7c) Oxygen (O)

i) 8 protons

ii) 8 neutrons

iii) 8 electrons

7d) Neon (Ne)

i) 10 protons

ii) 10 neutrons

iii) 10 electrons

7e) Calcium (Ca)

i) 20 protons

ii) 20 neutrons

iii) 20 electrons

7f) The lithium ion (Li⁺)

i) 3 protons

ii) 4 neutrons

iii) 2 electrons

7g) The sulfide ion (S²⁻)

i) 16 protons

ii) 16 neutrons

iii) 18 electrons

7h) The fluoride ion (F⁻)

i) 9 protons

ii) 10 neutrons

iii) 10 electrons

7i) The aluminium ion (Al³⁺)

i) 13 protons

ii) 14 neutrons

iii) 10 electrons

7j) The hydrogen ion (H⁺)

i) 1 proton

ii) 0 neutrons

iii) 0 electrons

7k) The nitride ion (N³⁻)

i) 7 protons

ii) 7 neutrons

iii) 10 electrons

8a) What are isotopes?

Isotopes are atoms of the same element that have the same atomic number but different mass numbers

8b) Why do isotopes occur?

Different atoms in the element can have a different number of neutrons in their nuclei

8c) What is the composition of a neon-20 atom and a neon-22 atom in terms of subatomic particles?

Neon-20: 10 protons, 10 neutrons, 10 electrons

Neon-22: 10 protons, 12 neutrons, 10 electrons

8d) Define relative atomic mass (Ar)

Relative atomic mass is the average MASS of all the isotopes in an element, taking abundances into account, relative to 1/12th of the carbon 12 isotope

8e) Why are relative atomic masses of elements rarely whole numbers?

Relative atomic masses are average values of all isotopes in an element

8f) What analytical technique is used to measure the relative atomic mass of elements /relative molecular mass of compounds?

Using a mass spectrometer

8g) Give three uses of this analytical technique

1. Separate isotopes

2. Trace out a mass spectrum

3. Measure relative atomic/molecular masses

9a) A sample of the element gallium is composed of 60.1% gallium-69 and 39.9% gallium-71. Calculate the relative atomic mass of gallium.

(60.1 × 69 + 39.9 × 71) / 100 = 69.798

9b) Using a mass spectrometer it was found that a sample of neon contained three isotopes: 80% of Ne-20, 10% of Ne-21, 10% of Ne-22. Calculate the relative atomic mass of neon.

(80×20 + 10×21 + 10×22) / 100 = 20.3

9c) 19.9% of the atoms in a sample of boron have five neutrons and 80.1% of the atoms in the sample have six neutrons. Calculate the relative atomic mass of boron.

Boron atomic number=5, so mass numbers: 10 and 11

(19.9×10 + 80.1×11) / 100 = 10.801

9d) Neon has two major isotopes, Neon-20 and Neon-22. Out of every 250 neon atoms 225 will be Neon-20 and 25 will be Neon-22. What is the average atomic mass of Neon?

(225×20 + 25×22) / 250 = 20.2

9e) Nitrogen is made up of two isotopes, N-14 and N-15. Given the relative atomic mass of nitrogen is 14.007, what is the percentage abundant of each isotope?

Let x = % N-14, (100-x) = % N-15

(14x + 15(100-x))/100 = 14.007

x = 99.3% N-14, 0.7% N-15

10ai) How many electrons can an s-orbital hold?

2

10aii) How many s-orbitals are there in a s-sublevel?

1

10aiii) How many electrons can an s-sublevel hold?

2

10aiv) How many electrons can an n = 1 energy level hold?

2

10bi) How many electrons can a p-orbital hold?

2

10bii) How many p-orbitals are there in a p-sublevel?

3

10biii) How many electrons can a p-sublevel hold?

6

10biv) How many electrons can an n = 2 energy level hold?

8

10ci) How many electrons can a d-orbital hold?

2

10cii) How many d-orbitals are there in a d-sublevel?

5

10ciii) How many electrons can a d-sublevel hold?

10

10civ) How many electrons can an n = 3 energy level hold?

18

11a) What is the Aufbau principle?

Electrons must fill the lowest available sub-levels first in terms of energy

11b) Why do electrons fill the 4s sublevel before filling the 3d sublevel?

The 4s sublevel is lower in energy than the 3d sublevel

11c) What is Hund’s rule?

When two or more orbitals of equal energy are available the electrons must fill the orbitals singly before filling them in pairs

11d) What is Pauli’s exclusion principle?

Two electrons in an orbital must have opposite spin

12ai) The Nitrogen atom

1s² 2s² 2p³