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Alkali Metas vs. Halogens
Transcript of Alkali Metas vs. Halogens
Halogens (group 7)
Alkali Metals (group 1)
good conductors of electricity
grey shiny surfaces when freshly cut with knife
very reactive metals
form ionic bonds
Reactively increases down the group.
Form ionic compounds with non metals
Atom to Atom (intramolecular) forces
Alkali metals bond using metalic bonds. A metalic bond gets weaker as you go down the group, because as the atomic radius increases the cations become father apart causing the sea of delocalized electrons to decrease.
Reactivity increases as you go down the group because the electron are farther away from the nucleus, which causes more shield by the electron in the inner orbitals making the hold on that electron weaker therefore it is easier for the electron to be ionization as shown in the first ionization.
Specific Physical Properties of the Alkali Metals
Place the alkali metal in a small beaker containing distilled water: Litium will float and slowly react, sodium reacts with a vigorous release of hydrogen and Potassium reacts more vigorouly to produce enough heat to ignite the hydrogen produced. The other Alkali metals are not commonly found and not allowed for students to mix, the video shown below show what happens when the Rubidium and Caesium react in water.
Chemical test for identification
Mix the element with highly concentrated hydrochloric acid and then hea:
lithium (Li/Li+) the flame will be crimson/ red
sodium (Na/Na+) the flame will be yellow
potassium (K/K+) the flame will be violet/lilac
comparison of physical properties between halogens and alkali metals
The Alkali metals are grey and shiney solids, while the Halogens range all different colours and states they are solid, liquid and gas. Both group form ionic compound but only Halogens for covalent bonds. THe Alkali metals have low densities while the Halogens have high densities and the melting point and boiling point patterns are opposite for the Halogens it increases whereas for the Alkali metals it decreases.
Comparison of forces
Comparison of reactions
The Alkali metals and Halogens are the same distance apart for the nobal gases causing everything to be opposite in terms of properties but there is also many similarities in their reactivity because they either need to gain or lose only one electron. The form the same ionic bond to become stable and have a full outermost orbital.
They show gradual change from gases, to liquid, to solid.
very reactive non-metals. Reactively decrease down the group.
form ionic compounds with meatls or covalent compounds with other non-metals
Atom to Atom (intramolecular) forces
Halogens are non-metals so they form covalent bond with other non metals. Halogens form the strongest kind of bonds when they react with the a metal. Covalent bonds where they share the electron with another non-metal. However like the Alkali metals form ionic bonds.
Typical reaction types
Reaction with Alkali metals: forms an ionic halide, halogen gains one electron causing both the Alkali metal and nobal gas to b stable.
Displacement reaction: relative reactivity, the take an electron from a negative ion of an element with weaker attraction to return that element to it original state.
Halogens have an oxidation state of -1. Although if the halogen is bonded to oxygen or to another halogen that is more electronegative, its oxidation state will not be -1.
Chemical test for identification
Halides- Halogens form salts with silver, adding a halide solution to a solution with silver produces a precipitate which can be used to identifying (by colour of precipitate, and sensitivity to light) the halide this is shown in the video below.
Van der Waals forces between (intermolecular) molecules increase with an increase in number of electrons
This shows that all of the elements in the alkali family have one electron in the s sub-section corresponding to the period they are in. This causes the metals to be highly reactive because as also shown they have one more electron then the closest nobal gases and they want to be like the nobal gas and lose their electron cause high reactivity.
Comparison of electron configuration and reactivity
Both alkali metals and Halogens are very attractive and it is because they are on opposite sides of the periodic table. Halogens are in the p group needing 1 more electron to be full but Alkali metals are in the s group and need to lose 1 electron or gain 7 electrons to be at the end of the p sections again.
The colour are produced because the element is excited and changes energy levels and then falls back down to the second energy level producing visable light.
Specific physical properties of the atoms
The electron configuration of the halogens shows that the halogens have 5 electrons in the p sub-level corresponding to the periods are in. The p sub level has 3 orbitals so they can have 6 electrons and all of the halogens only have 5 so their is one unpaired electron. The halogens only need one more electron to be like the nobal gases causing them to be very reactive.
The reactivity of the halogens is that it decreases as you go down the group this is because the halogen want to react another electron, the closer the valence electrons are the the nucleus the less shielding and the stronger the pull making it possible for them to attract another electron.
Reaction with Halogen, forms an ionic halide, alkali metal loses one electron causing both the Alkali metal and nobal gas to be stable.
Alkali metals have oxidation states of 0 and +1. All the common compounds are based on the M+ ion. This is because the first ionisation energy of these elements is low, and the second ionisation energy much higher.
Both Halogens and Alkali metals for Ionic bonds often with each other but the Halogens can also form covalent bonds with each other. They bonds formed between the element themselves are very different Alkali metals form Metalic bonding with sheets of Metal and then a sea of electrons but Halogens use Van der Waals forces which is very similar to magnetic attraction.
The reactions the two family do are very interesting. They both form ionic bond with each other to have stable octets, but the Alkali metals are very reactive in water because they can lose their electron but the Halogens can't so their most common reaction is double displacement where they can gain an electron to have a full octet. The identification process both rely on a colour to tell apart the elements but with the Alkali's you heat the metal and the Halogens you create Halides.
Trends in the Periodic table
Alkali metals from Ionic bonds with non-metals by loosing one electron while a halogen or other non-metal gains one electrons.