How do you read the PERIODIC TABLE?

What is the ATOMIC NUMBER?oThe number of protons found in the nucleus of an atom

OroThe number of electrons surrounding the nucleus of an atom.

What is the ATOMIC WEIGHT?

oThe number of protons and neutrons in the nucleus of an atom.

An introduction to the hydrogen burning and the alpha particle

Nuclear Fusion

How do I find the number of protons, electrons, and neutrons in an element using the periodic

table?

o # of PROTONS = ATOMIC NUMBER

o # of ELECTRONS = ATOMIC NUMBER

o # of NEUTRONS = ATOMIC _ ATOMIC WEIGHT NUMBER

Atomic Structure

• Protons are positively chargedparticles, weighing 1 atomic mass unit

(1.67x10-24 grams) and located in the nucleus.

• Neutrons are neutrally charged particles, weighing approximately 1 atomic mass unit and located in the nucleus.• Electrons are negatively charged particles weighing zero atomic mass units and located in the various orbitals of the energy levels outside the atomic nucleus.

Subatomic ParticlesThe subatomic particles combine to form an atom

Proton:

Positively charged, one mass unit, located in nucleus

Neutron

Neutral, one mass unit, located in nucleus

Electron

Negatively charged, no mass, located in electron cloud (surrounding nucleus)

Basics of an Atomic Nucleus

An atom is defined by the number of protons it has in its nucleus

Atomic Number:

Number of protons

Atomic Mass:

Sum of neutrons and protons

Hydrogen Nucleus

Atomic Number: 1

Atomic Mass: 1

11

Atomic number (Z)

Atomic Mass (A)

H+

Main Sequence StarsMain sequence stars are like our sun

They have an balance between outward thermal pressure and inward gravitational pressure.

This balance is called hydrostatic equilibrium.

The outward push from thermal pressure

The inward push from gravity

The pressure is generated from the thermal energy from nuclear fusion in the core

Hydrogen BurningThe process of hydrogen burning occurs in the core of stars

It is also called ‘proton-proton fusion.”

It consists of 3 steps.

It requires temperature of 10 million K or hotter

This process is the longest stage in a star’s life

Proton – Proton FusionStep 1

Fusion: the combining of 2 or more atoms to create a new, larger atom

Hydrogen burning, or proton-proton fusion, occurs in main sequence stars.

Forms a Deteurium atom (“heavy Hydrogen atom”)

Atomic Number: 1

Atomic Mass: 2

+

+

+n

H

H

1

1

1

1

H2

1

Proton-Proton FusionStep 2

Deuterium nucleus combines with a regular Hydrogen nucleus

Forms a Helium-3 nucleus:

Atomic number: 2

Atomic mass: 3

+n

H12

11H +

He2

3 +n

+

Proton-Proton FusionStep 3

Two Helium-3 nuclei combine to form a Helium-4 nucleus

The Helium-4 nucleus:

Atomic number: 2

Atomic mass: 4

This is also known as an alpha particle

He2

+n

+

He23 +

n+

3He

24

+n

+n

+

+

Alpha ParticleThe 4He atom is known as an alpha particle

It is one of the building blocks of larger elements

He24

+

n+n

Atoms are made of subatomic particles.

These consist of protons, neutrons and electrons.

An atom is described by its atomic number and atomic mass.

The gravitational pressure in stars is balanced by an outward thermal pressure.

The energy is generated by nuclear fusion in stars.

Hydrogen burning is a nuclear fusion process which results in the formation of alpha particles (Helium-4 nuclei).

This occurs through proton-proton fusion, which is a 3-step process.

Summary

Red GiantsAs a star uses up its hydrogen, helium accumulates in its core, and will eventually burn.

The remaining hydrogen continues to burn in a shell around the core

The hydrogen-shell burning increases the thermal pressure, which causes the star to expand into a Red Giant.

Triple-Alpha Process: Step 1

The fusion of He-4 (alpha particles) is also called alpha fusion.

In a triple-alpha process, typical of many red giants, the helium atoms combine to form carbon.

In the first step, two alpha particles combine to make Be-8 nucleus

(A= 8; Z= 4)

Triple-Alpha Process: Step 2

In the second step of the triple-alpha process, one alpha particles combines with the Be-8 nucleus to form a C-12 nucleus

(A= 12; Z= 6)

Super Giant StarsMore massive stars (>5 solar masses) can evolve to become Super Giants.

These are important in the synthesis of heavier elements up to iron (Fe).

In these stars, alpha fusion continues past the triple-alpha process. This forms a chain of alpha processes that result in subsequently heavier nuclei.

Chain of Alpha ProcessesThis chain of Alpha Processes is also termed the alpha ladder.

In this, an alpha particle is added to an atomic nucleus (such as carbon) to form oxygen.

The addition of an alpha particle to an atom adds 2 protons (and therefore the atomic number of the product is 2 larger than the original)

12 C + 4 He → 16 O

16 O + 4 He → 20 Ne

20 Ne + 4 He → 24 Mg

24 Mg + 4 He → 28 Si

24 Si + 4 He → 32 S

32 S + 4 He → 36 Ar

36 Ar + 4 He → 40 Ca

40 Ca + 4 He → 44 Ti

44 Ti + 4 He → 48 Cr

48 Cr + 4 He → 52 Fe

Carbon BurningOxygen Burning

Silicon Burning

Formation of Odd Elements

Odd elements are not formed through the alpha ladder in stars.

The Oddo-Harkins rule states that even numbered elements are inherently more stable (and therefore more common) than odd elements.

Odd elements can be formed during the Big Bang, radioactive decay or supernova nucleosynthesis.

IsotopesIsotopes are atoms of the same atomic number, but different atomic mass.

This is because they have a different number of neutrons.

All isotopes of the same element have the same number of protons

(This is necessary, because an elements identity is based on the proton number)

After hydrogen fusion, larger stars can continue with the fusion of heavier elements.

Red Giants can fuse helium and form carbon (triple-alpha process).

Super Giant Stars can form elements from later steps of alpha fusion.

The alpha ladder can form the even elements lighter than iron.

The odd elements can be formed in supernova or through nuclear decay.

Even elements are more common than odd elements.

After a star is exhausted of energy, its core will consist of Fe(and outer shells of lighter elements).

Summary