What were Döbereiner's Triads proposed in 1829?
Groups of three elements with similar chemical properties and middle atomic mass as the mean of the other two.
What did Newlands' Law of Octaves state in 1866?
Certain properties repeated every eighth element when arranged by increasing atomic mass.
How did Mendeleev arrange elements in his periodic classification?
By increasing atomic mass.
What periodic function did Mendeleev state for elements' properties?
Physical and chemical properties were periodic functions of atomic masses.
Which new elements did Mendeleev predict?
Scandium, gallium, and germanium.
How did Mendeleev's work help the study of elements?
It enabled systematic study and helped correct some atomic masses.
What were Mendeleev's major defects in his periodic classification?
Anomalous pairs, hydrogen's position, and difficulty placing isotopes.
Who showed atomic number is more fundamental than atomic mass?
Henry Moseley showed it.
What does the modern periodic law state about element properties?
They are periodic functions of atomic numbers.
How does the long-form periodic table arrange elements?
By increasing atomic number across 18 groups and 7 periods.
What similarity do elements in the same group share?
They have similar electronic configurations and properties.
Which elements does the s-block contain based on electron configuration?
Elements whose last electron enters an s-orbital.
What is the general electron configuration of s-block elements?
ns¹ or ns².
Which groups do s-block elements occupy in the periodic table?
Groups 1–2.
Which orbital does the last electron enter in f-block elements?
An f-orbital.
What is the general electron configuration of f-block elements?
(n−2)f¹–¹⁴(n−1)d⁰–¹ns².
Which element series are included in the f-block?
Lanthanides and actinides.
What are three characteristics of the d-block elements?
Variable valency, coloured compounds, and catalytic properties.
Where are metals mainly located on the periodic table?
On the left side of the periodic table.
What physical state and properties do metals generally have?
They are generally solid, malleable, ductile, and conducting.
Where are non-metals mainly located on the periodic table?
On the right side of the periodic table.
In what physical states can non-metals be found?
They may be solid, liquid, or gas.
Where do metalloids occur on the periodic table?
Along the zig-zag boundary between metals and non-metals.
Which elements are classified as metalloids?
B, Si, Ge, As, Sb, and Te.
What is the shielding effect in atoms?
It is the reduction of nuclear attraction on an outer electron by inner electrons.
What is the formula for effective nuclear charge?
Z_eff = Z - σ, where Z is nuclear charge and σ is shielding constant.
What is the shielding constant for a 2p electron in fluorine?
The shielding constant σ is 3.80.
What is the effective nuclear charge for a 2p electron in fluorine?
Z_eff equals 5.20.
How does effective nuclear charge change across a period?
It increases across a period.
How does effective nuclear charge change down a group?
It increases only slowly down a group.
How does effective nuclear charge behave for many outer electrons down a group?
It remains approximately constant for many outer electrons.
Why does atomic radius decrease across a period?
Because nuclear charge and effective nuclear charge increase while shell number stays constant.
Why does atomic radius increase down a group?
Because the number of electron shells increases while effective nuclear charge does not increase much.
Why are metallic radii similar in third-row and second-row d-block elements?
Because of lanthanide contraction caused by poor shielding of f-orbitals.
Why are anions larger than their parent atoms?
Because added electrons increase electron–electron repulsion.
Why are cations smaller than their parent atoms?
Because they have fewer electrons while nuclear charge remains the same.
What defines isoelectronic species?
They have the same number of electrons.
Give an example of isoelectronic species with 10 electrons.
F⁻, Na⁺, and Mg²⁺ each have 10 electrons.
How does ionic size change in an isoelectronic series as nuclear charge increases?
Ionic size decreases as nuclear charge increases.
What is ionisation enthalpy?
Energy needed to remove an electron from a gaseous atom or ion.
What is the first ionisation process formula?
X(g) → X⁺(g) + e⁻
What is the second ionisation process formula?
X⁺(g) → X²⁺(g) + e⁻
Why do successive ionisation enthalpies increase?
Because removing electrons from more positive ions is harder.
How does ionisation enthalpy change across a period?
It generally increases across a period.
How does ionisation enthalpy change down a group?
It generally decreases down a group.
Why is Be's ionisation enthalpy higher than B's?
B loses a 2p electron more easily than Be loses a 2s electron.
Why is N's ionisation enthalpy higher than O's?
Paired 2p electrons in O cause extra repulsion making electron removal easier.
What is electron gain enthalpy?
The enthalpy change when a gaseous atom gains an electron to form an anion.
How does electron gain enthalpy change across a period?
It generally becomes more negative across a period.
How does electron gain enthalpy change down a group?
It generally becomes less negative down a group.
Why do noble gases have zero or positive electron gain enthalpies?
Because they already have stable ns²np⁶ electron configurations.
Why is oxygen's electron gain enthalpy less negative than sulfur's?
Because the added electron enters the compact n=2 level causing greater repulsion.
What is electronegativity?
The tendency of an element in a molecule to attract shared electrons toward itself.
Which element has the highest electronegativity on the Pauling scale?
Fluorine with a value of 4.
Why does electronegativity increase across a period and decrease down a group?
Because effective nuclear charge increases across a period and atomic radius increases down a group.
How is valence generally related to outermost electrons in representative elements?
Valence is generally related to the number of outermost electrons.
What is H-type valency related to in representative elements?
H-type valency is related to eight minus the number of outermost electrons.
What are the common valencies for groups 1, 2, 13, and 14?
They are 1, 2, 3, and 4 respectively.
What valencies do groups 15, 16, and 17 commonly show?
They commonly show valencies 3/5, 2/6, and 1/7 respectively.
What is the definition of oxidation state?
Oxidation state is the charge acquired by an atom based on electronegativity.
How do groups show oxidation states across a period?
Groups show characteristic positive or negative oxidation states with gradual changes across a period.
Teste tes connaissances avec un QCM de 28 questions sur Periodic Properties.
1. What characterized Döbereiner's Triads?
2. What pattern did Newlands' Law of Octaves identify when elements were arranged by increasing atomic mass?
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