Sifat dan Kegunaan Alkali Tanah | Kimia SMA | Tetty Afianti

Summary

This chemistry lesson focuses on Alkali Earth Metals, explaining their position in the periodic table, properties, and uses. The instructor provides clear explanations about the electron configurations of these elements, which help in understanding their chemical behavior. A mnemonic is introduced to aid in memorizing the group members. Key properties such as reactivity with water, thermal conductivity, and ion formation are discussed, along with real-life applications in industries like construction, medicine, and fireworks. The lesson also includes an explanation of hard and soft water, with practical examples to distinguish between different alkali earth metal ions in a lab setting.

Takeaways

• 😀 Alkaline earth metals (Group 2A) include Be, Mg, Ca, Sr, Ba, and Ra, all having 2 electrons in their outermost shell, leading to +2 charge when ionized.
• 😀 These metals are relatively soft but harder than alkali metals, and they conduct heat well, except for beryllium, which is an exception.
• 😀 Alkaline earth metals react with water to form strong bases, except for beryllium, which has weaker reactivity.
• 😀 Radium is the only radioactive element in the alkaline earth metal group.
• 😀 Alkaline earth metals can form important compounds like duralium (used in aircraft), magnesium hydroxide (used in antacids), and calcium carbonate (used in cement).
• 😀 Hard water, or 'air sadah', is caused by dissolved minerals like calcium and magnesium, making it difficult for soap to lather and forming scum.
• 😀 Hard water is classified into two types: temporary hard water (which can be softened by boiling) and permanent hard water (which requires treatment with sodium carbonate).
• 😀 The presence of calcium and magnesium ions in hard water can cause scaling in boilers and pipes, leading to energy inefficiency.
• 😀 Excess calcium and magnesium from hard water can also lead to kidney stones if consumed over time, as they may precipitate and form deposits in the body.
• 😀 Reactions between alkaline earth metal ions and various reagents (e.g., sodium carbonate, sodium hydroxide) help distinguish between different ions based on precipitate formation.
• 😀 Practice questions in the script explore how to differentiate between ions like Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺ based on their reactions with reagents like NaOH and Na₂CO₃.

Q & A

What are alkali earth metals and where are they located in the periodic table?

Alkali earth metals are the elements located in group 2A of the periodic table. They are known for forming basic (alkaline) compounds and are found in the Earth's crust, often in insoluble mineral forms.

Why are alkali earth metals reactive at standard temperature and pressure?

Alkali earth metals are reactive at standard temperature and pressure because they have two valence electrons, which they easily lose to achieve a stable electron configuration similar to that of the nearest noble gas.

What is the general trend in the atomic radius and ionization energy of alkali earth metals as you move down the group?

As you move down the group from beryllium to radium, the atomic radius increases, and the ionization energy decreases. This is due to the addition of electron shells as you go down the group, making it easier to remove the valence electrons.

What mnemonic is used to help memorize the order of alkali earth metals?

The mnemonic 'Beli mangga hai hai hai lalu sharing Hai sirsak Hai Bawa rambutan the lounge Hai' is used to remember the order of alkali earth metals: Beryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr), Barium (Ba), and Radium (Ra).

What are some physical properties of alkali earth metals?

Alkali earth metals are generally soft, though harder than alkali metals. They conduct heat well (except for beryllium), and they react with water to form strong bases (except for beryllium, which reacts weakly). They also have relatively low melting and boiling points.

What is the significance of radium among the alkali earth metals?

Radium is the only alkali earth metal that is radioactive. It can emit radiation, making it unique compared to other metals in the group.

How do alkali earth metals react with non-metals?

Alkali earth metals tend to form ionic compounds when reacting with non-metals. The metals lose two electrons to form positive ions, while the non-metals gain these electrons to form negative ions.

What are some common applications of alkali earth metals?

Alkali earth metals are used in various applications, such as magnesium in alloy production (duralium), calcium carbonate in cement, and barium compounds in fireworks. Magnesium hydroxide is used in medicines, and strontium is used in fireworks and flares.

What is the difference between hard water and soft water, and how is it related to alkali earth metals?

Hard water contains dissolved salts of calcium and magnesium, which are alkali earth metals. These ions react with soap to form insoluble precipitates, making it harder for soap to lather. Soft water, on the other hand, has fewer of these ions.

How can the hardness of water be reduced?

The hardness of water can be reduced by heating (to remove temporary hardness caused by calcium bicarbonate) or by adding sodium carbonate (washing soda) to precipitate calcium and magnesium ions, removing permanent hardness.