Chapter 4 Science

Thomson's Experiments.

- In his experiments, Joseph John Thomson used a seal tube containing a very small amount of gas. - When the current was turned on, the disks became charged, and a glowing beam appeared in the tube. - Thomson hypothesized that the beam was a stream of charged particles that interacted with the air in the tube and cause the air to glow. - Thomson observed that the beam was repelled by the negatively charged plate and attracted by the positively charged plate.

Comparing Subatomic Particles

-Everything scientists know about subatomic particles is based on how the particles behave in experiments. Scientists still do not have an instrument that can show the inside of an atom. -Protons and neutrons have almost the same mass. About 2000 electrons equal the mass of one proton. - Protons and neutrons are found in the nucleus. Electrons are found in the space outside the nucleus.

Evidence for Energy Levels

-Scientists can measure the energy gained when electrons absorb energy and move to a higher energy level or measure the energy released when the electron moves to a lower energy level. Light is a form of energy that can be observed. The movement of electrons between energy levels explains the light you see when fireworks explode. Heat causes some electrons to move higher energy levels. - When those electrons move back to lower energy levels, they release energy. Some of that energy is released as visible light.

Discovery of the Nucleus

-The alpha particles whose paths were deflected must have come close to another charged object. The closer they came, the greater the deflection. - However, many alpha particles passed through the gold without being deflected. These particles did not pass close to a charged object. - Thomson's model did not explain all of the evidence for Rutherford's experiment. Rutherford proposed a new model.

Isotopes (continued)

-With most elements, it is hard to notice any differences in the physical or chemical properties of their isotopes. Hydrogen is an exception. ~ Hydrogen-1 has no neutrons. (Almost all hydrogen is hydrogen-1.) Hydrogen-2 has one neutron, and hydrogen-3 has two neutrons. Because a hydrogen-1 atom has only one proton, adding a neutron doubles its mass.

When magnesium burns, it combines with oxygen. In magnesium oxide, the ratio of the mass of magnesium to the mass of oxygen is always about ___________. Magnesium dioxide has a fixed composition.

3:2

neutron

A _______________ is a ___________________ subatomic particle that is found in the nucleus of an atom. It has a mass almost exactly equal to that of a proton.

Proton

A _______________ is a positively charged particle that is found in the nucleus of an atom. Each proton is assigned a charge of 1+. Each nucleus must contain at least one proton.

What contributions did Rutherford make to the development of atomic theory?

According to Rutherford's model, all of an atom's positive charge is concentrated in its nucleus.

Electron

An ________________________ is a negatively charged subatomic particle that is found in the space outside the nucleus. Each electron has a charge of 1-. The particles that Thomson later discovered were called electrons.

Bohr's Model of the Atom

As did Rutherford's atomic model, Bohr's atomic model had a nucleus surrounded by a large volume of space. But Bohr's model focused on the electrons and their arrangement.

How are atoms of one element different from atoms of other elements?

Atoms of different elements have different numbers of protons.

Rutherford's Hypothesis

Based on Thomson's model, Rutherford hypothesized that the mass and charge at any location in the gold would be too small to charge the path of an alpha particle. He predicted that most particles would travel in a straight path from their source to a screen that lit up when struck.

Protons

Based on experiments with elements other than gold, Rutherford concluded that the amount of positive charge varies among elements.

Electron Cloud Model

Bohr's model was improved-as scientists made further discoveries. Bohr correctly assigned energy levels to electrons, but electrons do not move like planets in a solar system. - Today, scientists use probability when trying to predict the locations and motions of electrons in atoms. - The electron cloud model replaced Bohr's vision of electrons moving predictable paths.

What was Dalton's theory of the structure of matter?

Dalton proposed the theory that all matter is made up of individual particles called atoms which cannot be divided.

different

Different elements emit ____________________ colors of light because no two elements have the same set of energy levels.

What is the most stable configuration of electrons in an atom?

Electrons are in orbitals with the lowest possible energies.

Ancient Greek Models of Atoms

If you cut a piece of aluminum foil in half, you have two smaller pieces of the same shiny, flexible substance. You could cut the pieces again and again. Can you keep dividing the aluminum into smaller pieces? Greek philosophers debated a similar question about 2500 years ago.

Neutrons

In 1932, the English physicist James Chadwick carried out an experiment to show that neutrons exist. Chadwick concluded that the particles he produced were neutral because a charged object did not deflect their paths.

like planets around a sun

In Bohr's model, electrons move with constant speed in fixed orbits around the nucleus, _______________________________. Each electron in an atom has a specific amount of energy.

Dalton's Theory

In a particular compound, atoms of different elements always combine in the same way. A theory must explain the data from many experiments. Because Dalton's atomic theory met that goal, the theory became widely accepted. over time, scientists found that not all of Dalton's ideas about atoms were completely correct. They revised the theory to take into account new discoveries.

A lithium atom has three electrons.

In the ground state, two of the lithium electrons are in the orbital of the first energy level. The third electron is in an orbital of the second energy level. If a lithium atom absorbs enough energy, one of its electrons can move to an orbital with a higher energy. This configuration is referred to as a n excited state. An excited state is less stable than the ground state. Eventually, the electron that was promoted to a higher energy level loses energy, and the atom returns to the ground state.

What is the difference between two isotopes of the same element?

Isotopes of an element have the same atomic number but different mass numbers because they have different numbers of neutrons.

Thomson's Model

Objects with like charges repel, or push apart. Objects with opposite charges attract, or pull together.

When some materials are rubbed, they gain the ability to attract or repel other materials. Such materials are said to have either a _______________________________________ electric charge.

Positive or negative

What properties can be used to compare protons, electrons, and neutrons?

Protons, electrons, and neutrons can be distinguished by mass, charge, and location in the atom.

What model do scientists use to describe how electrons behave in atoms?

Scientists use the electron cloud model to describe the possible locations of electrons around the nucleus.

1.) positive charge 2.) central area 3.) nucleus

The __1.)_______________ of an atoms is not evenly spread throughout the atom. - Positive charge is concentrated in a very small, _2.)__________________________. - The _3.)_____________________ of the atom is a dense, positively charged mass located in the center of the atom. -The total volume of an atom is about a trillion times the volume of its nucleus.

atomic number

The __________________ of an element is the number of protons in an atom of that element. - All atoms of any given element have the same atomic number. Each hydrogen atom has one proton in its nucleus. Hydrogen is assigned the atomic number 1.

mass number

The _____________________________ of an atom is the sum of the protons and neutrons in the nucleus of that atom. To find the number of neutrons in an atom, you need the mass number of the atom and its atomic number.

Atomic orbitals

The level in which an electron has the least energy-- the lowest energy--has only one orbitals. Higher energy levels have more than one orbital.

Democritus

The philosopher ___________________ believed that all matter consisted of extremely small particles that could not be divided. He called these particles atoms from the Greek word atomos which means "uncut" or indivisible."

energy levels

The possible energies that electrons in an atom can have are called ____________________.

Evidence for Subatomic Particles

Thomson concluded that the particles in the beam had a negative charge because they were attracted to the positive plate. He hypothesized that the particles came from the inside atoms because no matter what metal Thomson used for the disk, the particles produced were identical. The particles had about 1/2000 the mass of a hydrogen atom, the lightest atom.

Thomson's Model

Thomson revised Dalton's model to account for these subatomic particles. The atom has neither a positive nor negative charge, but there must always be some positive charge in an atom. -The atom is filled with a positively charged mass of matter that has negative charges evenly scattered throughout it.

What contributions did Thomson make to the development of atomic theory?

Thomson's experiments provided the first evidence that atoms are made of even smaller particles.

plum pudding

Thomson's model is called the " ___________________________" model. Today, it might be called the " chocolate chip ice cream" model. The chips represent negatively charged particles, which are spread evenly through a mass of positively charged matter-- the vanilla ice cream.

Protons Electrons Neutrons

What are three subatomic particles?

Energy Levels

When an atom gains or loses energy, the energy of an electron can change. An electron cannot exist between energy levels. An electron in an atom can move from one energy level to another when the atom gains or loses energy. Electrons gain or lose energy when they move between fixed energy levels.

John Dalton

_____________ studied the behavior of gases in air. Based on the way gases exert pressure, Dalton correctly concluded that a gas consists of individual particles.

Isotopes

_______________-are atoms of the same element that have different numbers of neutrons and different mass numbers. - To distinguish one isotope from another, the isotopes are referred by their mass numbers. For example, oxygen has 3 isotopes: oxygen-16, oxygen-17, oxygen-18. - All three oxygen isotopes can react with hydrogen to form water or combine with iron to form rust.

Aristotle

___________________ thought that all substances were made of only four elements -- earth, air, fire, and water. He did not think there was a limit to the division of matter. - For many centuries, most people accepted Aristotle's views on the structure of matter. By the 1800s, scientists had enough experimental data to support an atomic model.

Ernest Rutherford

___________________________ designed an experiment to find out what happens to alpha particles when they pass through a thin sheet of gold. Alpha particles are fast moving, positively charged particles.

All elements are composed of __________________.

atoms

An ______________________ is a visual model of the most likely locations for electrons in an atom.

electron cloud

An ___________________________________ is the arrangement of electrons in the orbitals of an atom.

electron configuration

When all the electrons in an atom have the lowest possible energies, the atom is said to be in its ___________________________.

ground state

Dalton measured masses of elements that combine when compounds form. The ratio of the masses of the elements in each compound was always the same. In other words, compounds ________________________________________.

have a fixed composition

All atoms of the same element have the same __________, and atoms of different elements have different masses.

mass

Compounds contain atoms of ______________________ element.

more than one

An ________________ is a region of space around the nucleus where an electron is likely to be found. The electron cloud represents all the orbitals in an atom.

orbital

An analogy for energy levels of electrons is a _____________________.

staircase -The landing at the bottom of the staircase is the lowest level. Each step up represents a higher energy level. The step height represents an energy difference between levels. You can only move in whole numbers of stairs. An electron may move up up or down two or more energy levels if it gains or loses the right amount of energy. - The size of the jump between energy levels determines the amount of energy gained or lost. - No two elements have the same set of energy levels.