Chemistry Essentials

Why atoms bond, react and behave the way they do

Chemistry Essentials is a Bertopia flashcard pack of 62 cards: why atoms bond, react and behave the way they do. It covers atoms and the periodic table; bonding and structure; reactions and energy; rates and equilibrium; acids, bases and solutions.

Sample cards

What decides which element an atom is?

The number of protons in its nucleus
The number of neutrons in its nucleus
The number of electrons in its outer shell
The total mass of the whole atom

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Answer

The number of protons in its nucleus

Atomic number, the proton count, defines the element. Changing neutrons gives isotopes; changing electrons gives ions. Both are still the same element.

What happens when sodium reacts with chlorine to form sodium chloride?

Sodium and chlorine share one pair of electrons equally between them
Sodium transfers an electron to chlorine, forming oppositely charged ions
Chlorine gives one of its electrons to sodium, making Cl⁺ and Na⁻
Both atoms lose electrons to the water and then repel each other

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Answer

Sodium transfers an electron to chlorine, forming oppositely charged ions

Sodium loses its single outer electron to become Na⁺, and chlorine gains it to become Cl⁻. The electrostatic attraction between the ions is the ionic bond.

Why must a chemical equation be balanced?

Atoms are not created or destroyed in a reaction
Reactants and products must have equal volumes
Every reaction needs equal moles on both sides
Molecules must keep their exact identity from one side of the equation to the other

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Answer

Atoms are not created or destroyed in a reaction

Conservation of mass means each element has the same number of atoms on both sides. Moles of molecules and volumes can change.

Why does raising the temperature speed up a reaction?

It lowers the activation energy needed for every single collision between particles
It increases the total number of particles in the flask
More particles have enough energy to react, and they collide more often
It makes the products more stable than the reactants

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Answer

More particles have enough energy to react, and they collide more often

Collision theory: higher temperature means faster particles, more frequent collisions and a larger fraction above the activation energy. The barrier itself is unchanged.

A solution has a pH of 3. What does that tell you?

It is alkaline, with a high concentration of OH⁻ ions
It is neutral, like pure water at room temperature
It is acidic, with a high concentration of H⁺ ions
It contains no hydrogen ions at all

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Answer

It is acidic, with a high concentration of H⁺ ions

pH below 7 is acidic. pH measures hydrogen ion concentration on a log scale; lower pH means more H⁺.

Carbon-12 and carbon-14 behave almost identically in chemical reactions. Why?

They have the same electrons; only neutron numbers differ
They have the same mass, so they react the same way
Carbon-14 loses its extra neutrons before reacting
Neutrons decide chemical behaviour, and both isotopes have six of them

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Answer

They have the same electrons; only neutron numbers differ

Chemistry is driven by electrons. Isotopes have the same protons and electrons but different neutrons, so they differ in mass and nuclear stability, not in bonding.

Sources

2 sources

OpenStax Chemistry 2e, OpenStax, Rice University
PubChem Periodic Table of Elements, US National Library of Medicine

Chemistry Essentials

Sample cards

Sources

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