🟡11. Явище періодичної зміни властивостей елементів на основі уявлень про електронну будову атомів

Summary

This video explores how the properties of elements and their compounds are governed by atomic structure and exhibit periodic trends. Key topics include atomic radius, metallic and non-metallic character, redox behavior, and acid-base properties of oxides and hydroxides. The video explains how atomic size decreases across periods and increases down groups, influencing metallicity and non-metallicity. It highlights the link between electron configuration and reactivity, showing that reducing agents are typically metals and oxidizing agents are non-metals. Using examples from the second and third periods, it illustrates trends in oxide and hydroxide acidity and basicity, providing a clear, systematic understanding of elemental behavior in the periodic table.

Takeaways

• 😀 Atomic properties and their compounds depend on the structure of atoms, which changes periodically.
• 😀 The atomic radius decreases across a period (left to right) due to an increase in nuclear charge, while it increases down a group (top to bottom) as the number of energy levels increases.
• 😀 Cations are smaller than their corresponding atoms because they lose electrons, while anions are larger due to gaining electrons.
• 😀 Metallic properties are stronger for larger atoms (with fewer valence electrons) and weaker as atomic size decreases. This trend increases down a group and decreases across a period.
• 😀 Non-metallic properties are stronger in smaller atoms with more valence electrons. These properties increase across a period and decrease down a group.
• 😀 Reducing agents, which give up electrons, correlate with metallic properties, while oxidizing agents, which gain electrons, correlate with non-metallic properties.
• 😀 Reducing properties increase down a group and decrease across a period, while oxidizing properties increase across a period and decrease down a group.
• 😀 Acidic properties of oxides and hydroxides strengthen across a period and weaken down a group, opposite to the trend for basic properties.
• 😀 Oxygen-free acids increase in strength down a group, while oxygen-containing acids follow the trend of increasing acidity across a period and decreasing down a group.
• 😀 In the third period, oxides and hydroxides change from basic (Na₂O, MgO) to amphoteric (Al₂O₃) and then to acidic (SiO₂, SO₃, Cl₂O).
• 😀 Metals are strong reducing agents (e.g., cesium), while non-metals like fluorine are strong oxidizing agents, located in opposite corners of the periodic table.

Q & A

What determines the properties of elements and their compounds?

The properties of elements and their compounds depend on the structure of atoms, which changes periodically across the periodic table.

How does atomic radius change across a period and down a group?

Across a period (left to right), atomic radius decreases due to increasing nuclear charge. Down a group (top to bottom), atomic radius increases because new energy levels are added.

Why are cations smaller and anions larger than their corresponding neutral atoms?

Cations lose outer electrons, reducing electron-electron repulsion and making the atom smaller. Anions gain electrons, increasing repulsion and enlarging the radius.

How are metallic and non-metallic properties related to atomic radius?

Metallic properties increase with larger atomic radius, as metals more easily lose outer electrons. Non-metallic properties increase with smaller atomic radius, as non-metals more easily gain electrons.

What are the trends in metallic and non-metallic properties across a period and down a group?

Across a period (left to right), metallic properties decrease and non-metallic properties increase. Down a group (top to bottom), metallic properties increase and non-metallic properties decrease.

Where are the most active metals and non-metals located on the periodic table?

The most active metals are in the lower left corner (e.g., cesium), and the most active non-metals are in the upper right corner (e.g., fluorine).

How do redox properties relate to metallic and non-metallic elements?

Reducing agents (donate electrons) are metals, while oxidizing agents (accept electrons) are non-metals. Reducing properties decrease across a period and increase down a group, whereas oxidizing properties increase across a period and decrease down a group.

How do the acid-base properties of oxides and hydroxides relate to element type?

Metal oxides and hydroxides are generally basic, non-metal oxides are acidic, and some elements form amphoteric compounds that exhibit both acidic and basic properties.

What trend is observed for the acidity of oxides across a period?

Across a period (left to right), oxides become more acidic, starting from basic oxides of metals, through amphoteric oxides, and ending with acidic oxides of non-metals.

How does the strength of oxygen-free acids change down a group?

The strength of oxygen-free acids increases from top to bottom within a group.

Give examples of oxide and hydroxide types for the third period elements.

Sodium oxide (Na2O) is basic → NaOH. Magnesium oxide (MgO) is basic but weaker → Mg(OH)2. Aluminum oxide (Al2O3) is amphoteric → Al(OH)3. Silicon oxide (SiO2) is acidic → H2SiO3. Sulfur trioxide (SO3) is acidic → H2SO4. Chlorine heptoxide (Cl2O7) is acidic → HClO4.

What general principle helps remember changes in properties along periods and groups?

Moving across a period and down a group results in opposite changes for most properties, such as atomic radius, metallic/non-metallic behavior, and acid-base characteristics.