C2- Development of the periodic table Flashcards
How was the periodic table structured before the 19th century?
Before the 19th century when subatomic elements had not yet been discovered, attempts to organize elements were based on atomic weight. Newland’s Law of Octaves, proposed by John Newlands in 1864, suggests that when elements are arranged in order of increasing atomic weight, every eighth element exhibits similar properties
Why was it incorrect to order the periodic table based on atomic weight?
The discovery of isotopes in the early 20th century explained why atomic weight wasn’t always a reliable indicator of an element’s position. Isotopes of the same element have different numbers of neutrons, leading to different atomic weight.
Why was Newland’s law of octaves discarded?
some elements were incorrectly placed based on their properties. The law also assumed a limited number of elements existed, which proved incorrect with further discoveries
How did Mendeleev organise the periodic table?
- Mendeleev organized his periodic table primarily by increasing atomic mass and also considering similar chemical properties of elements. He placed elements with similar chemical properties in the same groups and then arranged them horizontally across the table in order of increasing atomic mass. He also left gaps for undiscovered elements, based on his predictions of their properties.
Why are noble gases unreactive?
Noble gases are unreactive because their atoms already have complete outer electron shells, making them stable and not needing to gain, lose, or share electrons to achieve stability- they are chemically inert
how is the electronic structure of metals and non metals different?
Metals have a tendency to lose electrons and become positive ions (cations) whereas, non-metals have a tendency to gain electrons and become negative ions (anions)
can you explain the trend in the boiling points of noble gases?
-low melting and boiling points
-going down the group melting and boiling points increase because:
.increased atomic radius due to increased number of electron shells
.intermolecular forces are stronger
.more energy required to overcome forces
how does the difference in electronic structure of metals and non-metals affect their reactivity?
-for metals, reactivity increases as you go down the group because they have a tendency to lose electrons so, due to increase in atomic radius and shell shielding, electrostatic forces between nucleus and valence electrons decrease and it becomes easier to lose said electrons
- for non-metals, reactivity decreases as you go down the group because due to their tendency to gain electrons, as atomic radii and shell shielding increases and electrostatic forces weaken, it becomes harder to gain electrons
Why do group 1 metals have low density?
-alkali metals have less densely packed atoms due to their relatively large sizes
how do group 1 metals react with water?
All the alkali metals react vigorously with cold water. In each reaction, hydrogen gas is given off and the metal hydroxide is produced. The speed and violence of the reaction increases as you go down the group. This shows that the reactivity of the alkali metals increases as you go down Group 1.
Why do the first three alkali metals float on water?
The first three Group 1 elements (lithium, sodium, and potassium) float on water because they have a density less than 1 g/cm³. This means they are less dense than water, which has a density of 1 g/cm³
How can you show that hydrogen and metal hydroxides are produced when a group 1 metal reacts with water?
proof for Hydrogen:
-Fizzing
-Squeaky Pop Test:
If collected, hydrogen gas can be tested with a burning splint, which will produce a squeaky pop as it ignites.
proof for metal hydroxide:
-you can tell when an alkaline has been produced by the change in indicator colour (universal indicator turning purple)
What are the names of the first three alkali metals?
Lithium
Sodium
Potassium
What are the names of the first four elements in group 7?
Fluorine
Chlorine
Bromine
How do you recognise a halogen displacement reaction?
A halogen displacement reaction is recognized by observing a more reactive halogen displacing a less reactive halogen from a solution of one of its salts. This is often indicated by a colour change in the solution as the displaced halogen forms.
What are the main properties of the halogens?
-diatomic: form molecules of two atoms
- 7 valence electrons
-at room temp, the state of the halogens changes as you go down the group:
chlorine is a gas
bromine is a liquid
iodine is a solid
- density increases going down the group
-reactivity decreases going down the group
-melting and boiling points increase as you go down the group
Why are alkali metals soft?
They have one valence electron which is relatively far from the nucleus due to their large atomic size leading to a large atomic radii and is therefore not strongly attracted to it. This results in a weak hold by the nucleus on the electron, which in turn leads to weak metallic bonding which contributes to their malleable nature
What are the properties of the transition metals?
- high melting and boiling points
-form coloured compounds
-can act as catalysts
-less reactive than group 1 metals - different ion possibilities
How do transition metals react with oxygen, water and chlorine
oxygen: forms a metal oxide
water: forms a metal hydroxide+ hydrogen
chlorine: forms a metal chloride
Why is mercury not considered a traditional transition element?
Transition elements, are defined by having an incomplete d-subshell either in the neutral atom or in their common ions. This incomplete d-subshell is what leads to their typical properties, like forming coloured compounds and having multiple oxidation states. Because mercury doesn’t have an incomplete d-subshell, it does not form coloured compounds, exhibit variable oxidation states, or act as a catalyst in the same way as other transition metals, it isn’t considered to be one. Additionally, mercury is a liquid at room temperature, which is another unusual property compared to the typical high melting points of transition metals.
