Atomic Structure and the periodic table - Summary

Question 1

Q: What is the radius of an atom?

Answer 1

About 0.1 nanometres (1 × 10⁻¹⁰ m)

Question 2

Q: What is the radius of the nucleus?

Answer 2

Less than 1/10,000 of the atom’s radius

Question 3

Q: What determines the atomic number?

Answer 3

The number of protons

Question 4

Q: What determines the mass number?

Answer 4

Total number of protons and neutrons

Question 5

Q: What does the number of electrons determine?

Answer 5

The chemical properties and reactivity of the element

Question 6

Q: What was Dalton’s model of the atom?

Answer 6

Atoms as solid spheres that cannot be divided

Question 7

Q: What did the plum pudding model suggest?

Answer 7

Atoms are spheres of positive charge with embedded electrons

Question 8

Q: What did the gold foil experiment show?

Answer 8

Most alpha particles passed through → atom mostly empty

Some deflected → small, dense, positive nucleus

Question 9

Q: What was Bohr’s contribution to atomic theory?

Answer 9

Electrons orbit the nucleus in fixed shells

Question 10

Q: Why was the neutron discovery important?

Answer 10

Explained extra mass in the nucleus

Question 11

Q: Do isotopes have the same chemical properties? Why?

Answer 11

Yes, same number of electrons

Question 12

Q: Do isotopes have different physical properties? Why?

Answer 12

Yes, different masses (e.g., boiling point)

Question 13

Q: Example: Calculate Ar for chlorine (75% Cl-35, 25% Cl-37)

Answer 13

(35 × 75 + 37 × 25) ÷ 100 = 35.5

Question 14

Q: How do you determine electron configuration from atomic number?

Answer 14

Fill shells: 2, 8, 8 (for first 20 elements)

Question 15

Q: What is the electron configuration of sodium (Na)?

Answer 15

2,8,1

Question 16

Q: How is electron configuration linked to reactivity?

Answer 16

Atoms react to achieve full outer shells

Question 17

Q: What does the group number tell you?

Answer 17

Number of electrons in outer shell

Question 18

Q: What does the period number tell you?

Answer 18

Number of electron shells

Question 19

Q: Why do atoms form ions?

Answer 19

To get a full outer shell (stable configuration)

Question 20

Q: What is the ion formed by oxygen?

Answer 20

O²⁻ (gains 2 electrons)

Question 21

Q: What is the ion formed by aluminium?

Answer 21

Al³⁺ (loses 3 electrons)

Question 22

Q: What’s the difference between an atom and an ion?

Answer 22

Ions have unequal numbers of protons and electrons

Question 23

Q: How do Group 1 and Group 7 elements behave in reactions?

Answer 23

Group 1 lose 1 electron

Group 7 gain 1 electron

Question 24

Q: Why do Group 0 elements not form ions?

Answer 24

They already have a full outer shell

Question 25

Q: What is the charge on Group 2 and Group 6 ions?

Answer 25

Group 2: +2 Group 6: -2

Question 26

Q: Which part of the periodic table forms cations?

Answer 26

Left side (metals)

Question 27

Q: Which part forms anions?

Answer 27

Right side (non-metals)

Question 28

Q: What is the formula of calcium chloride?

Answer 28

CaCl₂

Question 29

Q: What is the formula of aluminium oxide?

Answer 29

Al₂O₃

Question 30

Q: Why are ionic compounds neutral overall?

Answer 30

Total positive and negative charges must balance

Question 31

Q: How are brackets used in ionic compound formulae?

Answer 31

For polyatomic ions, e.g., (SO₄)²⁻ in MgSO₄

Question 32

Q: What is the formula for magnesium nitrate?

Answer 32

Mg(NO₃)₂

Question 33

Q: What problem did Mendeleev’s table solve?

Answer 33

Grouped elements by properties, left gaps for undiscovered ones

Question 34

Q: How did Mendeleev predict undiscovered elements?

Answer 34

By patterns in properties and atomic mass

Question 35

Q: What confirmed Mendeleev’s predictions?

Answer 35

Discovery of elements with matching predicted properties

Question 36

Q: What is the difference between Mendeleev’s and modern table?

Answer 36

Modern is arranged by atomic number, not mass

Question 37

Q: What are periods and groups?

Answer 37

Periods: rows Groups: columns with same number of outer electrons

Question 38

Q: What happens when halogens react with metals?

Answer 38

Form salts (ionic compounds)

Question 39

Q: What is a displacement reaction?

Answer 39

More reactive halogen displaces a less reactive one from a compound

Question 40

Q: Example of displacement reaction:

Answer 40

Cl₂ + 2KBr → 2KCl + Br₂

Question 41

Q: What are the colours of halogens?

Answer 41

Fluorine: pale yellow gas Chlorine: green gas Bromine: red-brown liquid Iodine: grey solid (sublimes to purple gas)

Question 42

Q: What are the physical properties of Group 1 elements?

Answer 42

Soft Low density Shiny when freshly cut

Question 43

Q: What happens when alkali metals react with water?

Answer 43

Form metal hydroxide + hydrogen gas E.g., 2Na + 2H₂O → 2NaOH + H₂

Question 44

Q: Why does reactivity increase down the group?

Answer 44

More electron shells → more shielding → weaker attraction → easier to lose electron

Question 45

Q: What is the flame colour for potassium?

Answer 45

Lilac

Question 46

Q: How are transition metals different from Group 1 metals?

Answer 46

Harder and stronger Higher melting points Less reactive Form coloured compounds Have variable oxidation states Used as catalysts

Question 47

Q: Examples of coloured compounds?

Answer 47

Cu²⁺: blue Fe²⁺: pale green Fe³⁺: brown

Question 48

Q: Examples of catalysts?

Answer 48

Iron in Haber process Nickel in hydrogenation of alkenes