5. Joseph John Thomson published the idea
that electricity was in particles that were
part of the atom. Experimenting with
cathode rays, he established the mass and
charge properties of these particles. These
particles were named electrons. In 1904, he
came up with the plum-pudding model, which
was an idea of what the atom looked like
based on his experiments.
Electrons
Positively charged matter
J. J. Thomson (1897)
Thomson’s Plum Pudding Model
6. Ernest Rutherford (1911)
Ernest Rutherford, Johannes
"Hans" Wilhelm Geiger, and Ernest
Marsden noticed from their
experiments, that alpha particles would
sometimes bounce off at a high angle
when made to penetrate a very thin gold
foil. Their experiment is referred to as
the alpha particle scattering
experiment.
7. Using a setup similar to the Figure below, Rutherford and his
coworkers, after doing a series of experiments, observed the
following:
Most alpha particles were undeflected.
Some are deflected at smaller angles.
Few alpha particles deflected almost back towards the
source.
8. Nuclear Atom
Rutherford discovered protons and the nucleus.
He called the center of atoms the nucleus.
He showed that atoms have (+) particles in the
center, and are mostly empty space.
9. Niels Bohr (1913)
Niels Bohr, proposed that
the electrons existed only at
fixed distances from the nucleus
at set “energy levels,” or quanta.
Bohr also proposed that the
electrons “jumped” between
energy levels by absorbing or
releasing discrete amounts of
energy.
10. Bohr’s Model
Rutherford discovered protons and the nucleus.
He called the center of atoms the nucleus.
He showed that atoms have (+) particles in the
center, and are mostly empty space.
Niels Bohr improved on
Rutherford’s model. Every atom
has a specific number of
electron shells. He proposed
that electrons move around the
nucleus in specific layers, or
shells.
12. 01
02
03
Instead of orbits, there were orbitals or
regions of space with high probability
of finding electrons. These are
sometimes known as electron clouds
or electron subshells whose shapes
are described by complex wave
equations.
There is no real “empty space,” but
there are regions with a high or low
probability of finding an electron.
Instead of electrons being particles in the
model, electrons have characteristics of
both waves and particles.
Quantum Model
13. James Chadwick
In 1932, James Chadwick bombarded
beryllium atoms with alpha particles and an
unknown radiation was produced. Chadwick
interpreted this radiation as being composed
of particles with a neutral electrical charge
and the approximate mass of a proton. This
particle became known as the neutron. With
the discovery of the neutron, an adequate
model of the atom became available to
chemists.
17. • Atoms in their stable state are neutral; their
number of protons and electrons is equal.
• The mass of an atom is solely due to the mass of
the proton and neutron.
• The protons and neutrons are referred to as
nucleons.
• The nucleons which are tightly packed together,
form the nucleus within the center of the atom.
• Thus, much of the mass of an atom is
concentrated in the nucleus.
20. 6. Who developed the first atomic model?
7. Who discovered the particle neutron?
8. Who proposed the idea that electrons move around the
nucleus in specific layers or shells.?
9. Who discovered protons and the nucleus?
10.What are the two subatomic particles located within the
nucleus of an atom?
21. The Number of Subatomic Particles
in Atoms, Ions and Isotopes
22. What are neutral atoms?
A single atom is said to be electrically
neutral if its number of electrons (e-) is equal to
the number of protons (p+). Thus, an element’s
atomic number (Z) also specifies the number of
electrons in a neutral atom.
Neutral Atom
Z = p+ = e-
24. Since the mass of an atom is concentrated in the
nucleus, the mass number (A) is equal to the sum of
the masses of the protons and neutrons.
Mass number (A) = number of protons (p+) + number of neutrons (n0)
A = p+ + n0
Atomic Number (Z) = number of protons (p+) = number of electrons (e-)
Z = p+= e-
Number of neutron (n0) = mass number (A) – number of protons (p+)
N0 = A – p+
25. Example: How many protons, electrons and neutrons are present
in boron?
Solution:
Mass number (A) = 11 and Atomic number (Z) = 5
Atomic number (Z) = number of protons (p+) = number of electron
(e-)
p+ = 5 and e- = 5
n0 = A – p+
n0 = 11 – 5 = 6
27. Identify the neutrons, electrons and
protons in the following elements:
1. Chlorine
2. Radon
3. Osmium
4. Radium
5. Gallium
6. Silver
7. Tungsten
8. Cadmium
9. Copper
10.Aluminum
28. What are ions?
Ions are electrically charged particles
formed when atoms lose or gain electrons.
Positive ions have lost electrons, and negative
ions have gained them.
A negative charge ion (anion) has more
electrons than protons.
A positive charge ion (cation) has fewer
number of electrons than protons.
29. For example:
A neutral lithium atom (atomic number 3) has 3 protons and
3 electrons. If the atom loses 1 electron, it becomes an ion
(cation) with a charge of +1:
charge of ion = number of protons (p+) - number of electrons (e-)
30. The charge of an ion is written with the positive or negative
sign after the number (as in 1+) and sometimes before it (as in +1).
When the charge of an ion is +1 or -1, the number 1 is normally
excluded, and the charge is written clearly as + or - .
31. Example 2: Determine the number of electrons,
protons and neutrons of fluorine ion (F−1).
Solution:
Given:
A = 19, Z = 9 and charge of ion = -1 (means gain 1
e-)
p+ = 9
e- = 9 + 1 (gain 1 e-) = 10
n0 = A – p+
= 19 – 9
= 10
33. Different isotopes can exist and these can be
identified by its respective mass number. Mass
number is the sum of the number of protons and
the number of neutrons in an atom.
Mass number of tritium = p+ + n0 = 1 + 2 = 3
34. Different isotopes can exist and these can be
identified by its respective mass number. Mass
number is the sum of the number of protons and
the number of neutrons in an atom.
Mass number of tritium = p+ + n0 = 1 + 2 = 3
35. The table shows the number of subatomic
particles of carbon isotopes.
37. 1. What is the element with an atomic number of 15?
2. How many protons does the atom of this element have?
3. How many electrons are there in an atom of aluminum (Al)?
4. Among the elements in the periodic table, which has the
smallest number of protons?
5. Among the elements in the periodic table, which has the
largest number of protons?
Directions: Refer to your periodic table and
answer the following questions.
Everything around us is made up of tiny particles called atoms
The word "atom" is derived from the Greek word, “atomos” or indivisible. Atom is the smallest unit of matter that retains the identity of the substance. Atom is thought to be the smallest particle of a given element.
When the idea of the atom was first proposed by the ancient Greeks, they thought it was a particle with no parts.
However, towards the 19th century, Joseph John Thomson discovered that atoms have negatively-charged particles, which he called electrons. This led him to propose a new model for the atom, which he called the plum pudding model. Thomson proposed that the negatively-charged electrons were embedded in a cloud of positive charge, as shown in Figure 1. Since plums and puddings are not commonly known in the Philippines, it may work better for you to use the other name for the model, the raisin bread model or a watermelon fruit model.
A group of scientists composed of Ernest Rutherford, Johannes "Hans" Wilhelm Geiger and Ernest Marsden tested Thomson’s model by bombarding a very thin sheet of gold foil with positively-charged alpha particles. a student of Thomson’s who was among many who studied radioactivity. In 1902, he worked in Thomson’s laboratory where he distinguished two kinds of radiation based on their penetrating power: α (alpha) and β (beta). He studied these types of radiation and
Rutherford theorized that the model proposed by Thomson did not explain the deflection of alpha particles, therefore, he devised his own model.
In the raisin bread model, the electrons having a very small mass, are scattered in a cloud of positive charge. In this region where the electrons are found, there was no area with a similar charge to the alpha particles that can be found that can cause its deflection. To account for the few deflections and the rare occasions of very large deflections, Rutherford, in 1911, suggested a different structure of the atom where all the positive charge and nearly all the mass of the atom were concentrated in a very tiny region called the nucleus, which is found at the center of the atom. The rest of the atom, where the tiny electrons with very small mass moved, was largely empty space through which the alpha particles could travel undeflected. This model replaced the one proposed by Thomson and is the model that we hold to this time, with respect to the placement of the nucleus in the atom.
tackled one of the big issues with the Rutherford model in 1913. The system proposed by Rutherford was unstable because, under classical physics, the spinning electrons would tend to be attracted to the positive nucleus and lose energy until they collapse into the center. Bohr
Every atom has a specific number of electron shells.
Atoms are composed of three types of particles and these are the protons, electrons, and neutrons. These components of the atom are referred as subatomic particles. Table 1 shows the properties of these subatomic particles. The nucleus, which is found at the center of the atom contains protons (positively charged) and neutrons (no charge). The outermost regions of the atom contain the electrons (negatively charged).
Many atoms become stable when their valence shell is filled with electrons or when they satisfy the octet rule (by having eight valence electrons).
6. JJ Thomson
7. James Chadwick
8. Neils Bhor
9. Ernest Rutherford
10. Protons and neutron
Previously, you have learned about the three subatomic particles; protons, electrons and neutrons; and how these are arranged in the currently accepted model of the atom. All atoms of an element contain the same number of protons in their nuclei. The number of protons in an atom of a given element is referred as atomic number, designated as Z. The number of protons must be equal to the number of electrons in an electrically neutral atom. However, when the number of protons and electrons is not equal, ions are formed.
. Mathematically,. Notice the atomic structure in Figure 6 on the next page. Do they have equal number of protons and electrons?
Notice the atomic structureNotice the atomic structure in Figure 6 on the next page. Do they have equal number of protons and electrons?
. Do they have equal number of protons and electrons?
For neutral atom,
Since, Atomic mass is also known as atomic weight.
Previously, you have learned about the three subatomic particles; protons, electrons and neutrons; and how these are arranged in the currently accepted model of the atom. All atoms of an element contain the same number of protons in their nuclei. The number of protons in an atom of a given element is referred as atomic number, designated as Z. The number of protons must be equal to the number of electrons in an electrically neutral atom. However, when the number of protons and electrons is not equal, ions are formed.
. Mathematically,. Notice the atomic structure in Figure 6 on the next page. Do they have equal number of protons and electrons?
Atoms may gain charges. This happens when electrons are lost or gained by the atom. When this happens, the atom becomes an ion. Both are formed when atoms gain or lose electrons.
The net charge of an ion is the difference between the number of protons and the number of electrons.
Figure 8 shows the shorthand notation of lithium ion. The superscript at the right denotes the charge of the ion wherein the number of electrons may be determined. The charge is zero (0) when there is no superscript shown.
To be stable an atom will gain, lose, or share electrons to complete the outer most energy level (electron shell).
Protons lose or gains "Chemistry of acids".
Isotopes can either form spontaneously (naturally) through radioactive decay of a nucleus (i.e., emission of energy in the form of alpha particles, beta particles, neutrons, and photons) or artificially by bombarding a stable nucleus with charged particles via accelerators or neutrons in a nuclear reactor.
Notice the data in Table 3. What makes the three isotopes of hydrogen different from each other?
For example, Tritium (H-3), has a mass number of 3. Referring to Table 3, its number of proton is 1 and 2 for neutrons, giving a total of three. Mathematically:
For example, Tritium (H-3), has a mass number of 3. Referring to Table 3, its number of proton is 1 and 2 for neutrons, giving a total of three. Mathematically:
Notice the differences in their number of neutrons, resulting to 3 different carbon isotopes.
