S1-L3: The Periodic Table of Elements Flashcards
What is Atomic mass?
- single atom mass
- ->total mass of protons + neutrons + electrons
Define mass number (figure 1)
-total protons AND neutrons in nucleus
Outline what atomic number is (figure 1)
- also known as proton number
- identifies element
- n. of protons in nucleus
What is Dobereiner’s “Law of Triads”?
- Arithmetic mean of atomic masses of 1st AND 3rd element in triad approx equal to 2nd elements atomic mass in that triad
- examples: Cl/Br/I–> weight 35.5/ 80/ 127
- 1817 scientist
What was the 1864 British chemist, Newlands “Law of Octaves”? (figure 2)
- If chemical elements arranged according to increasing atomic weight
- ->those with similar physical AND chemical properties occur after each of 7 element interval
What did Mendeleev do with the periodic table and what did it show?
- arranged elements in increasing relative atomic mass order
- ->found chemical properties of elements AND their compounds showed periodic trend (pattern in table)
Describe the organisation of the modern periodic table including the following features:
- periods
- groups
- noble gases
(figure 3)
- elements arranged in increasing order of atomic number (Z) from left to right across table
- Periods: horizontal rows
- groups: vertical columns
- noble gases: found right side of periodic table
- progression runs from metals to non-metals across each period
Outline and describe the “Periodic Law”
- formal statement: properties of elements are periodic functions of their atomic numbers
- ->when elements arranged in increasing atomic number there is periodic pattern in their physical AND chemical properties
What are “families of elements”?
- elements which share certain characteristics
- ->in terms of observable behavior & atomic structure
State the common periodic table classifications
- Alkaline metals
- alkaline earth metals
- transition metals
- lanthanides
- Actinides
- Nobel gas
- non-metals
- metalloids
Describe Alkali metals
- Group 1
- silver coloured/ soft metals
- highly reactive AND rarely find in elemental form in nature
Give some examples of alkali metals
-lithium (Li)/ sodium (Na)/ Potassium (K)
Briefly explain what Alkaline Earth metals are
- Silver coloured/ soft metals
- group 2
- reactivity similar to alkali metals
State some examples of Alkaline Earth metals
-Beryllium (Be)/ Magnesium (Mg)/ Calcium (Ca)
Describe Nobel gases and give some examples
- group 18
- V. reactive AND toxic
- gases OR low boiling/ melting points
- non-metallic
- chemically inert
- like Ne/ Ar/ Kr/ Xe
- exist as atoms
What are metalloids?
- have metal and non-metal properties
- 6 elements belong to this family (diagonal from B)
Which 6 elements are the metalloids?
-Boron (B)/ Silicon (Si)/ Arsenic (As)/ Tellurium (Te)/ Astatine (At)/ Oganesson (Uuo)
Briefly explain and describe transition metals (D-Block) are
- elements with at least one oxidation state
- -> has partially filled d-subshell
- metal melting/ boiling points AND high densities
- form coloured compounds AND complex ions (dissolved in water)
- valencies variable PLUS ions readily undergo oxidation/ reduction
- -> E.G: Fe2+ + e- –> Fe3+
- able to use e-‘s from outer two orbitals for combination with other elements
From the F-block of elements what are Lanthanides (including properties)?
- 15 elements with atomic number 57-71
- also known as rare earth metals
- shiny & silvery white
- easily stain when exposed to air
- high m/ b points
State some examples of Lanthanides
-Lanthanum (La)/ Lutetium (Lu)
Explain what Actinides are (include properties)
- 15 elements with atomic numbers 89-103
- v. dense metals with distinctive structures
- numerous allotropes
- -> plutonium has minimum 6 allotropes
- combine directly with most non-metals
Outline and describe non-metals
- Groups 14-16
- cant conduct electricity/heat well
- v brittle unlike metals ALSO cant roll in to wires/pound in to sheets
- exist as two/three states of matter at room temp- gases (O2) AND solids (C)
- no metallic sheen/ glow AND not reflect light
What are the general trends in properties of elements in the periodic table?
- all elements of given group have V. similar physical + chemical properties
- ->with regular graduation in properties moving top to bottom of group
- -> can also see patterns going across a period
What happens to the size of an atom as you descend down a group?
-increases
Outline the trend in metallic character in the periodic table
- increases moving top to bottom in group
- apparent in groups IVA/ VA & VIA
- begins with non-metals (C/N/O) and ends with metals (Pb/ Bi and Po)
What happens to reactivity down a group?
- metals more reactive descending group
- non-metals become less reactive down group too
Describe electron shells in terms of the periodic table (figure 4)
- n. of shells equal to period number to which element belongs to such as group 1
- going down group n. of e- shells increases by 1 each time
What is Valency?
-N. of chemical bonds formed by atom
Give the IUPAC definition of valency
-max n. of univalent atoms (like H) which may combine with atom of element under consideration/ with fragments/ for which atom of this element may be substituted
What is monatomic ion valency equal to and state some examples?
- equal to it’s charge
- (H+) valency is 1/ (O2-) valency is 2/ (K+) valency is 1/ (Al 3+) valency is 3
- some elements may have multiple valencies
- ->like phosphorus (P)/ Nitrogen (N)- valency is 3/5
- transition metals
What happens to the number of valence e-‘s down a group?
-N. of e-‘s in outer shell of atom unchanged
Outline what the valency of elements is equal to in relation to their group number
- groups I/III/IV –> valency equal to group number
- groups IV/ V/ VI/ VII/ VIII –> valency equal to (8 - group number)
State the steps which must be followed to write the formula of chemical compound using the examples of
Na2SO4 and CH4
1- write symbols for elements & ions: Na(SO4)/ C/ H
2- write valency above AND right of symbols: Na^+1 (SO4)^2- / C^4 / H^1
3- identify how many of each atom needed to make n. of bonds needed by each atom/ ion
–>write numbers to right and below of symbol
–>trick: reverse valencies
–> Na2SO4 AND CH4
Calculate the molecular mass of Calcium Carbonate; CaCO3
Ca=40/ C=12/ O=16
- so CaCO3
- -> 40 + 12 + 3(16)= 100
Define Empirical formula and give some examples
- expresses elemental composition of compound as ratio
- ->examples: water (HO)/ Hydrogen Peroxide (HO)/ Glucose (CH2O)
What is Molecular formula?
-exact n. of each atom type present in one molecule of compound
State some examples of molecular formula
-water (H2O)/ hydrogen peroxide (H2O2)/ Glucose (C6H12O6)
How can you calculate the empirical formula from experimental results? Use the following example:
Compound contains: 32.4% Na/ 22.5% S/ 45.1% O by mass. Calculate it’s empirical formula
1- Mass% (assuming 100g): Na= 32.4/ S= 22.5/ O= 45.1
2-relative n. of atoms (% mass/Ar): 32.4/23= 1.41
–>22.5/32= 0.7
–>45.1/16= 2.82
3- Divide by smallest number: 1.41/0.7= 2
–>0.7/0.7= 1
–> 2.82/0.7= 4
–>so empirical formula is Na2SO4
Use the answer from the same example previously to calculate the molecular formula of the compound
- RMM of this compound is 142 so molecular formulae
- -> empirical formula mass= (2x23) + 32 + (4x16)= 142
- ->RMM/142= 1
- ->therefore formula is Na2SO4
Calculation of % composition from a formula
Example: Formula of crystal ferrous sulphate is FeSO4.7H2O. What is the % of iron by mass in ferrous sulphate?
- 56 + 32 + (4x16) + 7x (2x1 + 16)= 278
- ->56 parts iron in 278 parts of compound
- ->so % of iron by mass:
(56x100) / 278 = 20.1%
Summary of lecture
- Periodic table: elements ordered by atomic number/ electronic structure
- can use to predict chemical AND physical of elements like reactivity/ valency
- write formula of compound using valency:
- ->calculate % mass of each element in compound from chemical formula
- ->calculate empirical AND molecular formulae of compound from its % mass composition
