ATOMIC MODEL
He proposed that atoms are solid, indivisible spheres — like billiard balls.
John Dalton
A chemical change always produces a
a new substance
What type of elements usually form ionic bonds?
metals and nonmetals
What type of elements usually form covalent bonds?
nonmetals and nonmetals
His experiment with a cathode ray tube led to the discovery of electrons.
JJ Thomson
Yeast makes bread dough rise by releasing bubbles that expand the dough. What evidence of a chemical change is observed here?
gas formation
What happens to electrons when an ionic bond forms?
Electrons are transferred from one atom to another.
In a covalent bond, how are electrons involved?
Electrons are shared between atoms.
In his gold foil experiment, he discovered that atoms have a small, dense, positively charged nucleus.
Ernest Rutherford
In the vinegar and baking soda balloon experiment, the balloon inflates due to carbon dioxide release. Why can’t the vinegar and baking soda return to their original state afterward?
Irreversibility
When sodium bonds with chlorine to form sodium chloride, which atom loses the electron?
Sodium loses the electron.
Two oxygen atoms form a molecule of O₂. How many pairs of electrons do they share?
They share two pairs
He proposed that electrons orbit the nucleus in fixed energy levels.
Niels Bohr
When yeast is added to dough and it rises, what gas is produced during the chemical change?
carbon dioxide (CO₂)
Magnesium forms an ion with a charge of +2. What does this tell us about its electrons?
It lost two electrons to achieve a stable electron configuration.
How many valence electrons do atoms usually try to have when forming covalent bonds?
Eight valence electrons
This model describes electrons as waves and uses probability to show where they are likely to be found.
Quantum Mechanical Model
Compare the curdling of milk and the inflation of a vinegar balloon. What common evidence of chemical change do both share?
Both show formation of a new substance that cannot be reversed.
When calcium (Ca²⁺) bonds with chlorine (Cl⁻), what is the correct formula of the compound?
CaCl₂
Which groups of elements does not participate in chemical bonding?
Noble gasses