Atomic Structure - Topic 1

Question 1

Describe the structure of an atom:

Answer 1

a nucleus (dense core at centre of atom) containing protons and neutrons, surrounded by electrons in shells

Question 2

What are the two main parts of an atom?

Answer 2

• Nucleus – very small centre
• Electron cloud region

Question 3

How are protons, neutrons and electrons distributed in an atom?

Answer 3

not evenly distributed

Question 4

How are electrons in atoms arranged?

Answer 4

in energy levels (shells) that orbit the nucleus

Question 5

How are electrons arranged on the shells of an atom?

Answer 5

• Electrons are as far away from each other as possible on each shell as they both have a negative charge and repel
• Electrons are paired up when spaces are taken up they can do this because they spin in opposite directions so there is an opposite quality to the 2 electrons allowing them to both be paired up despite them both having negative charges

Question 6

Relative mass of proton:

Answer 6

1

Question 7

Relative charge of proton:

Answer 7

+1

Question 8

Relative mass of neutron:

Answer 8

1

Question 9

Relative charge of neutron:

Answer 9

0

Question 10

Relative mass of electron:

Answer 10

1/1837 or negligible

Question 11

Relative charge of electron:

Answer 11

-1

Question 12

Why must atoms have an equal number of protons and electrons?

Answer 12

Atoms have no electrical charge (are neutral) therefore there must be an equal number of neutrons and protons, so that the positive and negative charges balance

Question 13

What is the size of the nucleus of an atom compared to the overall size of the atom?

Answer 13

very small

Question 14

What do atoms of the same element have?

Answer 14

the same number of protons

Question 15

What is the number of protons unique to and what does it determine?

Answer 15

The number of protons (atomic number) is unique to the particular element and determines what type of atom it is (element)

Question 16

Isotopes:

Answer 16

different atoms of the same element containing the same number of protons but different numbers of neutrons in their nuclei therefore also a different mass number

Question 17

Why is the relative atomic mass for chlorine 35.5?

Answer 17

• It is the average mass of the isotopes present
• A sample of chlorine contains a mixture of 75% chlorine-35 and 25% chlorine-37 and has a mass (RAM) that is the average of the masses of the isotopes (weighted according to the % of each isotope – Which isotope occurs more in nature which is why the mass is closer to 35 as it occurs more than the other isotope)
• Chlorine therefore has a relative atomic mass (RAM) of 35.5

Question 18

What is the atomic number?

Answer 18

(called the Proton number in physics) is the number of protons in an atom

Question 19

Mass number =

Answer 19

protons + neutrons

Question 20

Number of neutrons =

Answer 20

mass number (protons + neutrons) – atomic number (number of protons)

Question 21

What is the number of electrons on each shell?

Answer 21

2, 8, 8, 2

Question 22

What does the existence of isotopes result in?

Answer 22

• The existence of isotopes results in relative atomic masses of some elements not being whole numbers
• A sample of chlorine contains a mixture of 75% chlorine-35 and 25% chlorine-37 and has a mass (RAM) that is the average of the masses of the isotopes (weighted according to the % of each isotope – which isotope occurs more in nature which is why the mass is closer to 35 as it occurs more than the other isotope)
  
  • Chlorine therefore has a relative atomic mass (RAM) of 35.5

Question 23

What three particles are atoms made up of?

Answer 23

Atoms of all elements are made up of threefundamental particles:electrons,protonsandneutrons

Question 24

The structure of a particular atom can be found from two numbers that each atom has which are:

Answer 24

• Theatomic number(called the Proton number in Physics) is the number of protons in an atom
• Themass numberis the sum of the protons and neutrons

Question 25

What is the relative atomic mass?

Answer 25

the average mass of all isotopes of an element

Question 26

How do you calculate relative atomic mass?

Answer 26

Ar = [(relative isotopic mass 1 x %) + (relative isotopic mass 2 x %)]/100

Question 27

What is the mass number?

Answer 27

the sum of the numbers of protons and neutrons present in the nucleus of an atom

Question 28

How would an ion and an atom of an element react if they had the same number of electrons?

Answer 28

they would react similarly as they have the same number of electrons (isoelectronic)

Question 29

What was atomic theory according to Greek philosophers (before scientists)?

Answer 29

- Before scientists, Greek philosophers pondered about the universe - Ancient Greeks throughout that the entire universe (or the universe they knew of at the time) was made from five elements: earth, water, air, fire and aether - Ancient Greeks thought that each of these “elements” had their natural place in the order of things: earth liked to be on the bottom, then water, then air, the fire, with aether floating on the very top - They used this idea to explain why a stone (earth) sinks in water and why fire reaches upwards in air - Democritus, a Greek philosopher, disagreed - Democritus proposed that matter could not be divided into smaller pieces forever, matter was made from small, hard particles that he called “Atoms” from a Greek word meaning “indivisible”

Question 30

What did John Dalton say about atoms and when?

Answer 30

- In 1808 a scientist, John Dalton, stated that atoms are tiny, solid balls, like billiard bells - While he didn't change the idea of the atom, he introduced the first atomic theory

Question 31

What was John Dalton’s atomic theory?

Answer 31

1. Atoms are tiny indivisible particles 2. Atoms of one element are all the same 3. Atoms of different elements are different 4. Compounds are formed by combing atoms

Question 32

What did J.J Thomson discover and when and what was he the first scientist to show?

Answer 32

- In 1897 J.J. Thomson discovered electrons with cathode rays - He was the first scientist to show that the atom is made up of even smaller things - This knowledge changed the atomic model to the “plum pudding model” - Thomson thought of the electrons as raisins inside a sphere of positively charged pudding

Question 33

What did Ernest Rutherford publish and when?

Answer 33

in 1911, Ernest Rutherford published the results of his gold foil experiment (aka “Rutherford’s gold leaf experiment’)

Question 34

What was Ernest Rutherford’s gold leaf experiment in 1911?

Answer 34

- He sent a beam of alpha particles (which were known to be positive particles) at a thin piece of gold - Based on the plum pudding model, the alpha particles should have gone straight through the foil, at most deflecting by fractions of a degree - This did not happen - most of the alpha particle did go through (as expected) however some were scattered by a few degrees (more than expected) and some actually deflected backwards - Years later when commenting on this experiment Rutherford said, “It was quite the most incredible event that has ever happened to me in my life. It was almost as incredible as if you fired a 15-inch shell (cannon ball) at a piece of tissue paper and it came back and hit you.” - Rutherford couldn't believe the results of his experiments so her repeated them more than 100,000 times

Question 35

What did Ernest Rutherford conclude from his gold leaf experiment?

Answer 35

1. Since most of the alpha particles went straight through, the atom was 99% atom space. 2. Some of the alpha particles deflected back, there must be a very dense positive centre in the nucleus. He called the dense centre the “nucleus” (from a Latin word meaning “little nut”) and claimed it was made from positive particles he called “protons”. 3. Since some of the alpha particles repelled and deflected at different angles further indicated that alpha and the centre was the same charge - positive.

Question 36

What were the flaws of Ernest Rutherford’s model of the atom?

Answer 36

- the negatively charged electrons would be attracted to the positively charged nucleus - if the electrons were allowed to be anywhere on the outside of the nucleus, most of them would spiral into the centre of the atom, releasing energy as they did so - but atoms did not release that energy

Question 37

From thinking about the energy problems from Rutherford’s model, what did Niels Bohr propose?

Answer 37

- Niels Bohr propose that electrons move around in specific layers or “shells” - in a 1913 publication he stated that every atom has a specific number of electron shells and thus the atomic model was modified once-again to put the electrons in specific locations - this new model is sometimes referred to as the “Bohr Model”, in honour of Niels Bohr, and sometimes called the “Rutherford-Bohr model”, to acknowledge both scientists

Question 38

What did James Chadwick discover and when?

Answer 38

- James Chadwick performed numerous experiments and discovered neutral particle - In his 1932 publication, James Chadwick calls this particle the “neutron” and states that they are found in the nucleus with the protons - Since then, scientists have discovered that protons and neutrons are made up of even smaller things called quarks

Question 39

Provide a summary of the development of the model of the atom:

Answer 39

- Greek Philosophers (before scientists) used five elements to explain the world (earth, water, air , fire and aether) however Democritus disagreed and said matter was made from hard particles he called “Atoms” - 1808 - John Dalton introduced the first atomic theory - 1897 - J.J. Thomson discovered electrons using cathode rays, atomic model referred to as the “plum pudding model” - 1911 - Ernest Rutherford’s gold foil experiment - 1913 - Niels Bohr proposed electrons move round the atom in shells after seeing the energy problems with Ernest Rutherford’s model - 1932 - James Chadwick discovered neutrons - Since then scientists have discovered protons and neutrons are made up of even smaller things called quarks

Question 40

Atomic nucleus:

Answer 40

Positively charged object composed of protons and neutrons at the centre of every atom with one or more electrons orbiting it in shells

Question 41

Dalton model:

Answer 41

Dalton described atoms as solid spheres, stating that different spheres made up the different elements

Question 42

Electron:

Answer 42

- negatively charge subatomic particle which orbits the nucleus at various energy levels - has a negligible relative mass

Question 43

Proton:

Answer 43

- positively charged subatomic particles present in the nucleus of the atom - relative has of 1

Question 44

Neutron:

Answer 44

- neutral subatomic particle present in the nucleus of an atom - relative mass of 1

Question 45

Energy shell:

Answer 45

different energy levels in atoms/ions occupied by electrons

Question 46

Intermolecular forces:

Answer 46

- the forces which exist between molecules - the strength of the intermolecular forces impact physical properties like boiling/melting point

Question 47

Mass number:

Answer 47

total number of protons and neutrons in the nucleus

Question 48

What do atoms of the same element have the same of?

Answer 48

atoms of a given element have the same number of protons in the nucleus - this number is unique to that element