Tabel periodik Unsur bagian 1- Perkembangan Tabel Periodik Unsur- KIMIA SMA kelas 10 semester 1

Summary

This video delves into the development of the periodic table, starting with early grouping of elements into metals and non-metals. It highlights key contributions from scientists like Dobereiner, Newland, Mendeleev, and Moseley, who shaped our understanding of element organization. Dobereiner introduced triads based on atomic mass, while Newland's Octave Law grouped elements by similar properties. Mendeleev predicted undiscovered elements in his periodic table, though some inaccuracies were later corrected by Moseley, leading to the modern periodic table, which is now organized by atomic number. The video provides a thorough historical perspective on the periodic table's evolution.

Takeaways

• 😀 The periodic table of elements consists of 118 known elements that are categorized to make them easier to study and understand.
• 😀 Elements were initially grouped into two broad categories: metals, which conduct electricity, and non-metals, which do not.
• 😀 Johann Wolfgang Dobereiner (1829) proposed the 'Law of Triads,' where elements with similar properties are grouped in threes, with the middle element's atomic mass being the average of the first and third elements.
• 😀 John Newlands introduced the 'Law of Octaves,' stating that when elements are arranged by increasing atomic mass, every eighth element shares similar properties.
• 😀 Dmitri Mendeleev (1869) created the first periodic table arranged by atomic mass, predicting the existence of undiscovered elements and leaving gaps for them.
• 😀 Mendeleev's periodic table was remarkable because it predicted the properties of future elements, such as the discovery of gallium (eka-aluminum).
• 😀 A limitation of Mendeleev's table was the incorrect placement of elements like iodine and tellurium, which was later corrected by Henry Moseley.
• 😀 Henry Moseley (1913) used X-ray diffraction to prove that elements should be arranged by atomic number rather than atomic mass, resolving placement issues.
• 😀 The modern periodic table is organized by atomic number, with elements grouped into 18 columns (groups) and 7 rows (periods).
• 😀 Groups in the periodic table are categorized into representative elements (1A-8A) and transition elements (1B-8B), with the lanthanides and actinides placed separately below the main table.
• 😀 The periodic table continues to be an essential tool for understanding the relationships between elements and predicting their chemical behaviors.

Q & A

What is the purpose of grouping elements in the periodic table?

The purpose of grouping elements is to make it easier for humans to study and understand the elements, allowing for their better utilization for the benefit of humanity.

How were elements initially classified?

Initially, elements were classified into two major groups: metals and non-metals. Metals are elements that can conduct electricity, while non-metals cannot.

What is Dobereiner's contribution to the periodic table?

Dobereiner proposed that elements could be grouped into 'triads' based on similar properties and atomic mass. He observed that the atomic mass of the middle element in each triad is approximately the average of the first and third elements.

What is Newlands' law of octaves?

Newlands proposed the law of octaves, which stated that when elements are arranged by increasing atomic mass, every eighth element will exhibit similar properties to the first element of the previous group.

What was Mendeleev's contribution to the periodic table?

Mendeleev developed the periodic table by organizing elements according to increasing atomic mass and similar properties. He predicted the existence of undiscovered elements and left gaps in his table for them.

What is the significance of Mendeleev's prediction about undiscovered elements?

Mendeleev's predictions were later confirmed when undiscovered elements, such as eka-silicon (which turned out to be germanium), were discovered, validating his method of organizing the periodic table.

What were some weaknesses of Mendeleev's periodic table?

One weakness was that Mendeleev's table did not account for the newly discovered noble gases, and there was an incorrect arrangement of elements such as iodine and tellurium.

How was the issue with iodine and tellurium resolved?

The issue was resolved by Henry Moseley's work using X-ray diffraction. He showed that the atomic number, rather than atomic mass, should be used to arrange elements, leading to the modern periodic table.

What defines the modern periodic table?

The modern periodic table arranges elements by increasing atomic number and groups them based on similar chemical properties. This is a shift from earlier tables, which were based on atomic mass.

What are the groups and periods in the modern periodic table?

In the modern periodic table, elements are organized into 18 vertical columns known as groups and 7 horizontal rows known as periods. Groups are numbered from 1A to 8A (and 1B to 8B for transition elements). Periods represent the electron shells of the elements.