Tiêu đề EDX Topic 7 Alkali & halogens .pdf ✅

Topic ? Alkali Metals & Halogens 1
Group I: Alkali Metals Topic ? 2 Group I: Alkali Metals They are called group 1 elements as they all have one electrons in their outer shell They are called alkali metals as they react with water forming alkaline solutions Good conductors of heat and electricity Shiny but tarnish very quickly when exposed to air Soft Low density Low melting points Melting point decreases Density increases although not regularly. E.g. K/Na/Li are less dense than water so they will float Softness increases They are the most reactive metals as they need to lose only 1 electron to become stable & have a full outer shell of electrons As we go down the group they become more reactive They react quickly with oxygen forming oxides and they react rapidly with water forming hydroxides Sodium lithium & potassium are stored under oil in labs to prevent reaction with air and water. Rubidium and Caesium are so reactive they have to be stored in sealed glass tubes to prevent entry of air Physical Properties Chemical Properties Trends in Physical Properties down the group
3 Francium at the bottom of the group is radioactive Great care should be taken when handling these metals as a tiny bit of sweat would cause a reaction producing lots of heat and corrosive metal hydroxides Alkali metals react with halogens forming salts They form compounds with metal ions +1 and when reacting, they form white compounds that are soluble in water forming colourless solutions If we burn them in air using a Bunsen Burner: They react with water in an exothermic reaction forming alkaline solutions & hydrogen As we go down the group the reactions get more vigorous lithium floats, fizzes, moves around & gets smaller/dissolves Sodium melts, floats, fizzes rapidly, moves around, gets smaller Potassium melts, floats vigorously, moves around, gets smaller & ignites Rubidium and Caesium reacts more vigorously than potassium and can be explosive. The reaction is too hazardous to be conducted in a school lab. Observations of Alkali Metals with Water Lithium burn with a red flame to form lithium oxide Sodium burns with a yellow flame forming sodium oxide Potassium burns with a lilac flame forming potassium oxide Reactions with Water Sodium + Water --> Sodium Hydroxide + Hydrogen Potassium + Water --> Potassium Hydroxide + Hydrogen When asked to write observations in the exam, it is better to write ‘fizzing/bubbling/effervescing’ rather than ‘a gas is given off’ because fizzing/bubbling effervescing is what you actually see. Hint! Topic ?