Model of The Atom, Symbols, Relative Atomic Mass, Electronic Charge & Isotopes

What is the smallest part of an element that can exist?

An atom.

Who first proposed in 1803 that all matter was made of tiny, indivisible spheres called atoms?

John Dalton.

What subatomic particle did J. J. Thomson discover through his experiments?

The electron.

The _____ model of the atom, suggested by J.J. Thomson, describes the atom as a ball of positive charge with negative electrons embedded in it.

plum pudding

What experiment, designed by Ernest Rutherford in 1909, was used to test the plum pudding model?

The alpha particle scattering experiment.

In the alpha scattering experiment, what were the positively charged alpha particles fired at?

A thin sheet of gold foil.

What was the expected result of the alpha scattering experiment if the plum pudding model were correct?

All alpha particles were expected to pass straight through the foil.

What did the observation that most alpha particles passed straight through the gold foil indicate about the structure of an atom?

That an atom is mostly empty space.

What did the deflection of some alpha particles in Rutherford's experiment suggest about the atom's nucleus?

The nucleus must have a positive charge, as it repelled the positive alpha particles.

What did the observation that a small number of alpha particles bounced straight back from the gold foil imply?

That the mass of the atom is concentrated in a tiny central nucleus.

Rutherford's experiment led to the _____ model, which states the atom's mass is concentrated in a positively charged nucleus.

nuclear

Who adapted Rutherford's nuclear model by suggesting that electrons orbit the nucleus in specific shells or energy levels?

Niels Bohr.

Further experiments by Rutherford led to the idea that the nucleus contained small, positively charged particles called what?

Protons.

In 1932, who provided experimental evidence for the existence of neutrons in the nucleus?

James Chadwick.

What two types of subatomic particles are found in the nucleus of an atom?

Protons and neutrons.

What is the relative mass of a proton?

1.

What is the relative mass of a neutron?

1.

What is the relative mass of an electron?

Very small

What is the relative charge of a proton?

+1.

What is the relative charge of a neutron?

0 (neutral).

What is the relative charge of an electron?

-1.

Why does an atom have no overall electrical charge?

It contains an equal number of positive protons and negative electrons, so their charges cancel out.

Where is most of the mass of an atom concentrated?

In its nucleus.

What is the radius of the nucleus compared to the radius of an atom?

The radius of a nucleus is less than 1 / 10000 of the radius of the atom.

What term describes the number of protons in the nucleus of an atom?

Atomic number (or proton number).

What does the atomic number of an element determine?

Which element it is.

What is the term for the total number of protons and neutrons in an atom's nucleus?

Mass number.

How do you calculate the number of protons in an atom?

Number of protons = atomic number.

How do you calculate the number of electrons in a neutral atom?

Number of electrons = atomic number.

How do you calculate the number of neutrons in an atom?

Number of neutrons = mass number - atomic number.

A sodium atom has an atomic number of 11 and a mass number of 23. How many protons does it have?

11 protons.

A sodium atom has an atomic number of 11 and a mass number of 23. How many electrons does it have?

11 electrons.

A sodium atom has an atomic number of 11 and a mass number of 23. How many neutrons does it have?

12 neutrons (23 - 11).

What is the definition of an isotope?

Atoms of the same element with the same number of protons but a different number of neutrons.

Isotopes of a given element have the same atomic number but different _____ numbers.

mass

Why do all isotopes of an element have the same chemical properties?

Because they have the same number of electrons, which determines chemical properties.

The isotope Hydrogen-1 (¹₁H) has how many protons, electrons, and neutrons?

1 proton, 1 electron, and 0 neutrons.

The isotope Hydrogen-2 (²₁H) has how many protons, electrons, and neutrons?

1 proton, 1 electron, and 1 neutron.

What is the definition of an ion?

An electrically charged particle formed when an atom (or molecule) gains or loses electrons.

How does an atom become a positive ion?

By losing one or more electrons.

How does an atom become a negative ion?

By gaining one or more electrons.

A sodium atom (Na) has 11 protons and 11 electrons. How many protons and electrons does a sodium ion (Na⁺) have?

11 protons and 10 electrons.

An oxygen atom (O) has 8 protons and 8 electrons. How many protons and electrons does an oxide ion (O^2-) have?

8 protons and 10 electrons.

What is the term for the arrangement of electrons in shells or energy levels around the nucleus?

Electronic structure (or electronic configuration).

What is the maximum number of electrons that can occupy the first electron shell?

2 electrons.

For the first 20 elements, what is the maximum number of electrons that can occupy the second electron shell?

8 electrons.

For the first 20 elements, what is the maximum number of electrons that can occupy the third electron shell?

8 electrons.

What is the electronic structure of a sodium atom, which has 11 electrons?

2,8,1.

What is the electronic structure of an argon atom, which has an atomic number of 18?

2,8,8.

What is the electronic structure of a calcium atom, which has 20 electrons?

2,8,8,2.

Why are the elements in Group 0 (the noble gases) chemically inert or unreactive?

Because they have a stable arrangement of electrons with a full outer shell.

Atoms react to achieve a stable electronic structure, which usually means having a _____ outer shell.

full

What is the definition of relative atomic mass (A_r)?

A weighted average mass of the atoms of an element, taking into account the abundance of its isotopes.

Why are relative atomic masses, like that of chlorine (35.5), often not whole numbers?

Because they are a weighted average of the masses of an element's different isotopes.

What is the formula to calculate the relative atomic mass (A_r) of an element with two isotopes?

A_r = (a₁ × m₁) + (a₂ + m₂) / total abundance

Chlorine has two main isotopes: chlorine-35 (75% abundance) and chlorine-37 (25% abundance).

Calculate its relative atomic mass.

A_r = (75 × 35) + (25 × 37) / 100 = 35.5

Copper has two isotopes: copper-63 (69% abundance) and copper-65 (31% abundance).

Calculate its relative atomic mass to one decimal place.

A_r = (69 × 63) + (31 × 65) / 100 = 63.6

The chemical symbol for an element is a one or two letter code, where the first letter is always _____ and the second is always lowercase.

capital

A substance made up of only one type of atom is called an _____.

element

A substance formed from two or more elements chemically combined in fixed proportions is called a _____.

compound

The central part of an atom containing protons and neutrons is the _____.

nucleus

What is the one or two letter code that represents an atom of an element?

A chemical symbol.

What is the name for the different energy levels in an atom that are occupied by electrons?

Electron shells.

The number of electrons in the outermost shell of an atom determines its _____ properties.

chemical

A magnesium ion (Mg²⁺) is formed when a magnesium atom loses two electrons. If a Mg atom has 12 protons, how many electrons does the ion have?

10 electrons.