Expert Chemistry & Science Tutoring

Key Concepts and Definitions

• Atomic Number: The number of protons in the nucleus, determining the element's identity.
• Atomic Mass: The total number of protons and neutrons in the nucleus, expressed in atomic mass units (amu).
• Density: Mass per unit volume, measured in grams per cubic centimeter (g/cm³).
• Melting Point: The temperature at which a solid turns into a liquid.
• Boiling Point: The temperature at which a liquid turns into a gas.

Chemical Reactivity

• Reactivity describes an element's tendency to undergo chemical reactions.
• Highly reactive elements, such as sodium and chlorine, easily form compounds.
• Less reactive elements, such as gold and platinum, are more stable and less likely to react.
• The position of an element on the periodic table can provide clues about its reactivity.
• Elements in Group 1 (alkali metals) are highly reactive, while elements in Group 18 (noble gases) are the least reactive.

Periodic Trends

• Atomic Radius: Decreases across a period (left to right) due to increased nuclear charge.
• First Ionization Energy: Increases across a period due to stronger nuclear attraction.
• Electronegativity: Generally increases across a period and up a group due to increased nuclear charge and decreased atomic radius.

Worked Examples

• Example: Determine the atomic number and mass of an element with 10 electrons and 12 neutrons.
• Solution:
• Atomic number = number of protons = number of electrons = 10
• Atomic mass = number of protons + number of neutrons = 10 + 12 = 22

Common Mistakes

• Confusing atomic number and mass
• Using incorrect units when measuring density
• Assuming that all elements are equally reactive
• Ignoring periodic trends when predicting properties

Practice Problems

1. Calculate the density of an object with a mass of 25g and a volume of 10cm³.

2. Which element is more reactive, sodium or oxygen?

3. Explain why atomic radius decreases across a period.

Exam Tips

• Understand the concepts thoroughly.
• Practice solving questions and applying your knowledge.
• Familiarize yourself with periodic trends and memorize key data.
• Read the exam questions carefully and answer to the point.

FAQs

• What is the difference between atomic mass and molecular mass?
• How do you determine the number of neutrons in an atom?
• Which group of elements is known for its high reactivity?

Conclusion

Understanding the properties of elements is crucial for GCSE Chemistry. By grasping key concepts, recognizing periodic trends, and honing your analytical skills, you can excel in your exams and deepen your understanding of the fundamental building blocks of matter.